I think there is an important point to note in relation to this: which is that Appstore and Steam are similar ideas. i.e. a platform with games/software within easy reach and all purchasable via the same standard mechanism. But more crucially they also have a community aspect (less so Appstore I suppose) that means word spreads very quickly.

It would be interesting to see the same thing tried with a more standard retailer like Play.com or perhaps EA (with it's smaller store).

I have no idea of what would happen - but it would be interesting.