IMHO the "sandboxes" those OS'es provide are all terribly broken. You'll have to sign your code, you can't distribute your code outside of app shops (either completely impossible like on iOS, or scare-dialogs pop up like in OSX), there are gate keepers which dictate what software gets in the app shops and which don't, and which can remove your app from the shop at a whim. And did you look at the Windows8 Store Apps API? It's a f*cking joke. Innovation doesn't happen in those closed-down environments, only commerce (but commerce depends on innovation).