For what it's worth, Apple sees this as distinct from garbage collection. For new projects they recommend using ARC, even on the Mac where "real" GC is (and will continue to be) available.
(I haven't done any Mac OS programming with GC, so I really don't know anything about it, but I've always heard people say the GC is not all that great. So my own uneducated guess is that while GC is messy and complicated, ARC is simple & doesn't have any runtime overhead (they say in the docs that retain/release is now much faster, as is autorelease using the new syntax).)