Xcode might be without any cost, but the Apple hardware needed to legally run a copy of OS X (which also isn't free) - I don't really see how "Xcode being free" enters into it, as long as the software is distributed for iOS devices?

For the Mac app store, it might be different, as you need a Mac to access that anyway.

FWIW I think the issue here is that artificial limits on what code can be run on what hardware (legally) is in conflict with the (L)GPL -- and there's really nothing anyone other than Apple can do about it. Which is also why, as far as I know there's no actual legal way to distribute (L)GPL software on these locked app stores - there's no way for the distributor to actually honor the license, and so no way for them to be able to (re)use/distribute the code legally?