Sony says that because of security concerns it will not be offering Trophy support on the PSP.
Eric Lempel, Sony's director of PlayStation Network operations, put it very simply: "You're not going to see Trophies on the PSP," he said last week. Despite advances in its ongoing efforts against piracy, including the upcoming PSP Go which will download games directly from the PSN Store, Sony apparently has concerns that gamers will eventually come up with ways to manipulate their rankings and Trophies.
"If people can inflate their rankings and amounts of Trophies" across a shared Trophy system, it "kills the whole system," Lempel said, including the PlayStation 3. Sony's priority is "keeping it secure, keeping it fair," he added, and the only way to ensure that is to eliminate Trophies on the PSP.
As Develop points out, each iteration of the PSP has been successfully hacked and piracy on the system is rampant. But this decision may be more about the PlayStation 3 and ensuring its Trophy system isn't compromised than about the PSP itself; in that light it could also be seen as a tacit admission that despite its new design, Sony still has concerns that the PSP Go will be vulnerable to exploitation.