Do IDEs count? A lot of Mac users use Eclipse. It's not common among all-Mac teams that just do XCode, but it's fairly common for devs in groups that mostly do PC development to own Macbooks that they run Eclipse on.

Probably not a big concern for Apple, but it's common in universities, too, since Eclipse is (until now, at least) cross-platform enough that you can assume Windows/Mac/Linux-using students can all install it on their laptops.