By the reading, it appears that they still have a lot of slow G4s in the group. Given the PPC 970's vastly superior floating point performance (to both Intel and G4), likely 50% clock boost by the end of the year (with corresponding bus speed boost), and 10-20% speed increases due to the new compiler, the G5s should be really pumping up the OS X numbers through this year.
Superior performance which, thus far, remains officially undocumented. Where's the SPEC results, if it's so hot? Even Apple appears to have pulled those fakey-SPEC rate results from their website now.
From my own look at it, it appears to me that a single G5 is approximately on a par with a single P4, on a clock-for-clock basis, and so far I've seen nothing to disabuse me of that notion.
Anyway, for distributed computing - particularly distributed computing on someone else's computers, where I don't have to worry about how much they cost - individual node speed really doesn't matter, only aggregate performance, like I said. Given that there are five times as many HardOCP members as there are OSX members, the average PPC box will have to be five times faster than the average x86 box for Team OSX to match the performance of Team HardOCP. And that's just not happening. Even if the PPC team triples the work-unit-per-node performance of x86, which is wildly unrealistic, the fact that there are so many more x86 boxes still puts them way ahead. Team OSX may not fall behind as rapidly with new compilers and the like, but I expect that they'll still be falling behind, if for no other reason than because they're simply outnumbered.
Now, if we're shopping for a supercomputer, that might be a different story, but that's not the example we're presented with here.