One thing I recall is Linus is really big on "absolutely no noise whatsoever". The passively cooled but still reasonably powerful Air seems like ideal hardware for his tastes, at least for a laptop.
With the exceptionally good ARM hardware coming in from Apple, I can't see mainstream future for other laptops which will allow OS freedom. As time goes on, Apple should be able to significantly reduce the price of entry level Macbooks. Look at iPad pricing, entry level laptops just for iPad level work on a laptop form factor don't have to cost a lot.
I always thought this will be Chromebooks, and hoped Google would be more friendly to other OSs because of their past, but it looks like it will be Macbooks that will fill that space.