It sounds just like the Mac App Store to me, except at least you can buy real desktop apps from Apple's store.
The real typical MS tactic at work here is bundling their new tablet OS and app environment with desktop Windows to piggyback on the later's success. Making Metro for tablets only (even if it still had the ability to drop to the desktop) would probably leave them in the same situation that they're in with Windows Phone 7; a decent mobile OS/UI in distant third place because they were so late to the party.
As a desktop user, I can't stand the "integration" they've done between Metro and the desktop. I'd rather go "Full Metro" and use it like a graphics mode multitasking DOS (if only the apps had better/consistent keyboard support) than to be constantly shuffled between the two environments.