Apple chooses their words carefully. If you look at http://www.apple.com/iphone/technology/osx.html you'll notice that they repeatedly say "OS X." If you look at any other Apple document such as http://www.apple.com/macosx you'll notice that they always call their computer operating system "Mac OS X." My guess would be that Mac OS X is their full computer operating system, while OS X is a derivative/variant that is specifically their appliance operating system. Only time (and an eventual whitepaper on the Developer site) will tell the true differences. But the point is that there are differences even in the name.