I've felt this same frustration with POWER for what feels like forever. I'd love to build and run a POWER desktop system, but traditionally there hasn't been a readily available, standard form-factor, somewhat inexpensive motherboard that you could just order up from Tyan or whoever. On and off over the years there's been a lot of talk about how this company or that was going to build a standard ATX motherboard for POWER cpu's, but they seem to never materialize, or if they do, they're insanely expensive, or something which keeps the whole idea just out of reach.
This most recent push for openness in the POWER world might actually change that though. Tyan does have a kinda-sorta not-too-expensive POWER8 based server available, and there was a document floating around a while back listing all the companies who were committing to build machines, motherboards, etc. based on POWER8. As I recall, there were a lot of names on the list, which is encouraging.
But still... why can't we hit up NewEgg and order an ATX motherboard, a CPU and some RAM for, say, $1000.00 or less? sigh