@ Elwood:
As far as the majority (me included) of the Amiga users know, it's Amiga Inc. that's granting licenses to anything Amiga-related. So it's not such a weird question to ask.
Actually, if I've read the OS4 website from Hyperion (unfortunatley off-line now so I can't double-check, don't shoot me for creating false-hope) right and understood it right, Hyperion stated that OS4 could be re-compiled to other hardware as well. I don't know if they're the only people who decide on such a thing, guess Amiga Inc has a say in it as well. But I remember thinking at that time in the lines of: 'Okay, if I had a budget to pay 4 men-year development I could actually ask them to do a built on a platform.' I had to let go of the as I don't have that kind of money ;-)
So I think we would love to hear why we're on the PPC route and why AMD/ATi based is not an option... [could have named any combination, it's just an example]