Right, but this is largely orthogonal to the problems with Metro on the desktop. Sandboxed Mac App Store apps are limited, but need not be written against an entirely new set of APIs that is not only unsupported by previous versions of the OS, but unsupported by non-App Store apps running on the current OS version. Say what you will about the Mac App Store, it at least doesn't suffer from all the problems inherent in the iOS App Store model. Metro does.