Amiga has stated many times that they are not a hardware company. The PPC decision was made by Hyperion. I don't know about the chipset-specific decision, though it makes sense given the resources required to support multiple chipsets, and Eyetech was the only company to step up and provide hardware.
That is odd, because i can clearly recall that AmigaINC announced the so called zeca specs for the AmigaONE name. Also hyperion was not hired to port the OS before years after the AmigaONE and OS4 was announced. Hyperion didnt have any part in choosing the hardware, as it was all up to Amiga and Eyetech.