There are quite a bit of PPC users, and PS3 isn't just PPC but it also has the CellBE processor, the only one with such a thing. Thanks to IBM's axing of the Cell Blades, the only way to get 'em now is by buying a PS3!
OtherOS users would never ever need to crack the ps3 for pirated games; those in the industry actually think that Sony's move was stuipd because the pirates themselves had considered the PS3 too hard to crack, and thanks to OtherOS the hackers didn't care about hacking the thing.
In fact, the hackers stopped short of enabling piracy precisely because they weren't interested in that. It was the pirate community the one that went and used the opened doors to enable the "copy game to HDD, run from HDD" thingy. But they would still be unable to do so if the hackers hadn't cracked the thing, and the crack wouldn't have happened if OtherOS hadn't been disabled in the first place!
It may be a small % of PS3 users, but it is the kind of people that actually have the knowledge to crack the thing. Bad move!