Not entirely true.. for most low end PPC Macs this is true.. but for those with a Dual-Core or Quad G5 there is VLC Player which does allow video playback od Blu-Ray movies. Also, Toast 10 and Dragon Burn provide support for using blu-ray as a storage medium..
As for a native PPC Blu-Ray player, none exist to my knowledge, but VLC is the closest one can come to viewing blu-ray movies..
Again, I would recommend a blu-ray player for its emense storage primarily, but also for video playback on the last G5's and maybe, just maybe the last 1.42 MDD or FW800 G4. G5 would be highly recommended.