This really flips the argument that Mac hardware is overpriced and underpowered on its head. Now Apple computers are a premium product from a performance perspective, as well.
Apple is moving to basically ban non-Apple store installs of Mac software. It's been in progress the last few years but they are on the final stages of turning Macs into iPhones.
Probably not, since there are many crucial pro-level applications related to image editing, modelling and animation, video and audio production that realistically wouldn't be on the App Store (well, apart from Apple's own products).