"imho, people are voting with their money for bigger screens"

Bigger screens were partially a response to Apple's ability to lock up global "retina" LCD production. Unable to compete at ppi, they could compete on absolute resolution. They're certainly popular on their own merits though.

"and different/more exciting OS UX"

This seems a bit fanciful. Here's a better story: guy walks into a store, salesman steers guy towards model that gets him the bigger commission.