I agree that having Mac OS X run under virtual machines will make testing easier. One can only hope that Apple is moving in that direction. I doubt things will change any time soon though, because Apple makes money by selling hardware. You are allowed to run Leopard Server in a virtual machine now, but that's a completely different market where Apple could increase market share by allowing it.

License issues aside, to test on PPC architecture, one would need an emulator type of virtual machine. With PPC going the way of the dodo, I don't think anyone will be bringing a usable solution to market. We're stuck with keeping an old PPC machine around for a few years yet.