I can't seem to find it now to quote, but someone up above mentioned that as they've gotten older, they have less interest in romantic storylines, and I agree--although as I child it always irked me that even fairytales seem to end with a wedding. We have so many stories that end with "and they got married and lived happily ever after" -- it's the sort of thing where it builds the idea that to live happily ever after, one must marry, and therefore, one's happiness is dependent upon making sure others stay in your life. That always bugged me as a child, but  Lewis seems to like to stress that boys and girls can be friends for the long term and not necessarily become romantic (Digory and Polly, [book] Susan and Caspian, Eustace and Jill). These are important relationships to model for children, especially given many more stories lean toward all-roads-lead-to-romance.

Through a more cultural lens, while Lewis was very traditional in some ways, I think he also was a bit of a disruptor in others. Both couples buck the trend, so to speak: Digory and Polly don't fulfill the marry-the-girl/boy-next-door tradition, and Shasta, as Prince Cor, gets to marry who he likes, rather than marrying for political reasons (if he had, that would have been a very logical place for Lasaraleen to resurface, with Aravis becoming a diplomat and brokering the deal). Incidentally, we see the same thing with Caspian, where he marries someone who gives him no political connections, turning down the opportunity to build greater rapport with the Lone Islands by choosing a wife from there. Shasta and Aravis' marriage bucks the "happily ever after trend" in another way, too, given that the information is presented along the lines of "they fought and made up so well they got married so as to do it more conveniently".

Looking at things apologetically, I feel Lewis understood the idea that making your happiness or well-being depending on another is a modern form of idolatry. While he might have been a fan of "obey" in marriage vows, his writing tends to support the idea that each person is a fully formed, independent entity, and while people should support each other, ultimately, it is up to oneself to determine certain things about your person, including your relationship to G-d and where you find joy.

Posted by: @col-klink

It's also worth mentioning that C. S. Lewis wrote in Mere Christianity that he believed wives should obey their husbands and Polly should definitely not obey Digory. 

Sorry, could you clarify that please? Did Lewis write that Polly should definitely not obey Digory? 

Mere Christianity was published in 1952, after the wartime radio talks were compiled. The Magician's Nephew wasn't published until 1955, so I assume you don't mean he mentioned Polly & Digory specifically?