One reason i would say is that PS3 did not show any support for an HDD yet, so they are keeping themselves quiet until the PS3 is confirmed to have a hard drive. Theres no use otherwise.

The other factor i feel more likely is that PS3 wont come out for a while, and that if they release one for PS3 too soon, people will not buy their Xbox version in which some people are buying Xbox for and instead get PS3. So to not hurt MS or Sony, they are holding back.

Also they might just release more PS2 versions if the PS3 can handle it lol