@Martyn
Its not just that. Hyperion can't be expected to write drivers for, and support, all the different motherboards out there. Even if they just support a small subset, there are bound to be revisions, and "almost compatible" boards with similar chipsets, and when OS4 doesn't work properly, they'll blame Hyperion.
Also, Amiga software had already started migrating to PPC. It would be stupid to change tactic again and have to support THREE architectures!
There are various other good reasons, too, and a search of all the Amiga forums will bring them up. Its a very boring, tired and irrelevant argument.