Interesting question, perhaps he was implying it had some historical importance.

LWW happened just as WW2 was breaking out. I should imagine that the events of Magician's Nephew occurring right at the beginning of the century when Queen Victoria had not yet died, would give plenty of scope for interest. There is an association with the events when the tree finally did fall down in a very bad storm, even the previous behaviour of the tree when nothing was happening in UK. Then there is what the Professor did with it. Artistic style might be another reason if the wardrobe was a copy of, say, Chippendale furniture. Even before the Second World War, hand carved & decorated furniture were becoming rarer, paving the way for the minimalist factory style furniture of today. These days, wardrobes, themselves, are less common, due to more practical built-in cupboards with sliding mirror doors in all bedrooms.

That is my take on why Mrs Macready might show that particular wardrobe to visitors, but maybe, it was just that Mrs Macready had "heard something" & having caught up with them, wondered what those kids were "up to"?

Not even Digory had an inkling that the wardrobe was magical. I can imagine him telling his housekeeper the story of how it came to be (minus the Narnian story of course), and that she considered the piece of furniture an oddity.

"And this, ladies and gentlemen, is a wardrobe that is carved from the tree of the master's childhood home. For those of you who were in London during the great summer storm of 19-- you'll remember a great may trees falling due to the high winds. This was one of those trees. As the master of the house had such fond memories of this tree, he had it eternalized as a piece of furniture rather than chopping it up for firewood. Now. . . let's turn our attention to this blue-bottle in the window!!!"

Good one, Digory Kirke! More like "let's get away from this blue bottle on the window sill before anyone notices", muttered under her breath, with her hurrying her tourists to the next more important exhibition such as another suit of armour, hidden nearby. Or that painting of the famous crackpot relative of Professor Kirke's, better known by the name of Uncle Andrew, perchance?

I don't think people use wardrobes much today. I remember that we had a metal one in our house years ago. It wasn't like the beautiful piece of furniture in the Narnia books. Today people will more often store their clothes in closets since most houses and apartments are built with enough of them. A wooden wardrobe is probably more of a British/European thing (I don't think many Americans have one). It may seem rather quaint to most of us. I guess Lewis would have thought it more ordinary than we do, although this wardrobe was an unusual one with Narnia magic.

Why did Mrs. Macready show the tourists the spare room with the wardrobe in it?

Perhaps Aslan is one of the tourists Mrs. Macready is showing around and he directs her to it. (In human form...of course.) Herding the Pevensies, just like in HHB with Shasta, Aravis, Hwin, and Bree.

I don't think people use wardrobes much today. .... Today people will more often store their clothes in closets since most houses and apartments are built with enough of them. A wooden wardrobe is probably more of a British/European thing (I don't think many Americans have one).

This post is making my head dizzy - as far as I know, closets and wardrobes are the same thing, ie a cupboard with hanging space for clothes, either built into a bedroom or free-standing.

Do you have metal ones these days? I can't imagine anything except wood or wood veneer.

either built into a bedroom or free-standing.

Is that perhaps the difference between them? As a non-native speaker, I'm just guessing.

To me, a wardrobe is wooden and free-standing - but then possibly LWW was one of my first sources for learning that word

This post is making my head dizzy - as far as I know, closets and wardrobes are the same thing, ie a cupboard with hanging space for clothes, either built into a bedroom or free-standing.

As an American, my definition of a wardrobe is a piece of furniture that is tall and able to store hanging clothes. I have only ever seen a wardrobe once. It was for sale in a thrift store. I wanted to buy it but I was probably 13 at the time and had no money.
Almost all houses built in the last 100 years have closets with bars or rods to hang your clothes on. It's a separate room/space, not a piece of furniture. (Something like this.)
Furniture for storing clothes are dressers or drawers, but those are for folded items, not hanging items. (Like this....)

I'd agree with your two definitions at the end.

I think the answer is that while Americans distinguish between freestanding wardrobes and built-in closets, the British use the word 'wardrobe' for any type of clothes hanging & storage space, whether free standing or built in. Free standing preceded built-in ones, as I understand.

The latter link shows what I would call a chest of drawers, a tallboy, or (slightly bigger) a Scotch chest. They are for folded clothes or other items.

So all closets are wardrobes but not all wardrobes are closets?

I very much like the idea of a wardrobe being different from a closet. . . but maybe that's just the Narnian in me coming out.

The sheer uselessness of a free standing wardrobe in the era of modern housing pretty much precludes my ever purchasing one. . . unless one of my apple trees ever falls, in which case, I might just have to make one

In my previous UK residence, I had a freestanding wardrobe. The house was one of a row of four joined together, and fairly cheaply built in maybe 1980s. My family home (growing up in NZ, designed by UK carpenter/joiner) had built in wardrobes from the 1950s. My previous NZ house before the quakes was late 1970s, and had built in ones too. My current NZ house has built in ones, also from late 70s.
I'm now living in a late Victorian house in London which had a wardrobe built in when alterations were made upstairs. The late Victorian house where I stayed in December had built in ones.
And that's all I can tell you.

So all closets are wardrobes but not all wardrobes are closets?
The sheer uselessness of a free standing wardrobe in the era of modern housing pretty much precludes my ever purchasing one. . . unless one of my apple trees ever falls, in which case, I might just have to make one

That is a matter of when & where you are. Old houses that have never been renovated often are just the bare walls, apart from bathroom fittings & a stove. The buyer or renter is expected to supply his/her own storage facilities. Listening to a Bee Gee song (My old man's a dustman, he lives in a Council flat) I would be informed that extra stingy people, when they moved house, even took up the carpet, let alone wardrobes. When I married in the 1970's we could buy a bedroom suite which was basically a cupboard with lots of hanging space, plus a matching dressing table, & the accompanying double bed frame. The dressing table (or duchess) has a mirror slotted into the back of the chest of drawers. With mirrored doors now more practical, such mirrors aren't necessary any more.

This post is making my head dizzy - as far as I know, closets and wardrobes are the same thing, ie a cupboard with hanging space for clothes, either built into a bedroom or free-standing.

As an American, my definition of a wardrobe is a piece of furniture that is tall and able to store hanging clothes. I have only ever seen a wardrobe once. It was for sale in a thrift store. I wanted to buy it but I was probably 13 at the time and had no money.
Almost all houses built in the last 100 years have closets with bars or rods to hang your clothes on. It's a separate room/space, not a piece of furniture. (Something like this.)
Furniture for storing clothes are dressers or drawers, but those are for folded items, not hanging items. (Like this....)

Isn’t it too bad that many modern houses often do not have free standing wooden wardrobes? I suppose you could buy a a wardrobe on e-bay, but it might be very expensive. And unless it is from Narnia there probably isn’t any magic in it.