I'd bet 99.9% of people buying PC Laptops never upgrade a single chip... Apple's non-pro lines are likely not much different. Apple largely sacrificed that ability (in a few product lines) in favour of creating some of the thinnest laptops available. I don't remember them ever doing that before Macbook Air, for now reason.

That said, in this case, I don't see what is being gained by not making the GPU swappable or at least accessible (although it might very well still be). I'm assuming they could simply only offer official support for the one it contains but let people do whatever they want with it (which again might be the case in practice, they just aren't announcing it officially).