Steve: The Obj-C2 runtime is deeply reworked in places - it's certainly more than just syntactical sugar. I'm sure the GC could be back-ported to 10.4, but that makes another Obj-C environment for Apple to maintain (Obj-C, Obj-C+GC, Obj-C2, Obj-C2+GC) unless they also backport Obj-C2. Porting removes a small bit of leverage that they can use to tease developers to upgrade to 10.5.

I'd like it every bit as much as you would, but I'm not holding my breath.