It used to, but doesn't any more. Lack of demand.
And incase you're saying that PPC support is more important than the tens of thousands of devices linux supports, think again. I've never had a hardware setup ubuntu hasn't worked with. It can be tricky at times, but my digital camera works straight away, my phone does, my MP3 player, web camera, usb headset, usb/wireless mouse, etc etc etc. The hardware support in linux absolutely vast, and support for non-peripheral hardware is going to be pretty tight.
So yeah, linux supporting everything does mean lowest-common-denominator development, as the grandparent said.