They might have just targeted the 6.1 sdk and decided not to deal with the 6.0 issues. For new things it is actually a good idea as 6.1 is quite a bit better than 6.0 in things like core data.
https://developer.apple.com/library/ios/#releasenotes/Genera...
http://stackoverflow.com/questions/15550861/nssortdescriptor...
I find random differences far too often.