The last few hardware iterations and firmware updates to the PlayStation Portable have made the device share more in common with its console cousin, the PlayStation 3. This led some to speculate that Trophies would go cross-platform, letting players up their PlayStation Rank from games on either system. Not so, according to Sony's Eric Lempel in recent comments to Joystiq. "You're not going to see Trophies on the PSP," he said. It's pretty hard to misinterpret that.
The reasoning goes back to the PSP's ever-present piracy problem. It seems Sony figures that if the system's security allows it to be hacked so much, dubious methods would inevitably come up to "articially inflate rankings and the amount of Trophies." If Trophies are shared cross-platform and one of those platforms is compromised, Lempel says it "kills the whole system" and essentially makes the Ranks worthless. So once again, blame it on those filthy pirates for ruining your fun.

damn I wanted hack psp trophy's so I could be on top =]