But to answer your question, for one thing, I would hope they could play 1080p x264 streams. The Mac Mini does 720p (on MorphOS)
I know I'm OT here so please forgive me but, I have several G4 Macs, all running Mac OS X Snow leopard and not one of them can play 720p - not even close, it's like watching a slideshow.
On the Mac forums I frequent I was told that the G4, even at 1.5Ghz or 1.67Ghz just isn't fast enough to decode a 720p x264 stream in real-time. If that is the case, how can MorphOS play back the same stream on the same hardware?
