[wtracy]

If you're using multiple platforms, I could see the benefit of not having to enter your credit card multiple times. But honestly, if you're going to buy a program on your PC, then walk over to your Mac and buy it again, do you really care if you're buying it from the same store both times?

I know that Steam lets you take your games from one machine to another, but I don't expect that to be the norm for most app stores.

[esbwhat]

This is not how that works -- if you buy a game for windows on steam, the mac version is free. I've tried this personally, and I expect the same will be true for linux as well. In other words, pay once, get the game for all OS', updating automatically, and all connected to the same account so you can chat to windows and mac players through the steam client