Gamers are a funny old bunch - just take a look at the latest speculation surrounding a Sony Japan job advertisement that may or may not hint at the development of a PS4.
Old games on new platforms
As that includes both the PSP and the PS3, the inevitable conclusion they (and many others) have reached is that both a new PlayStation Portable and a PS4 are in the pipeline. After all, what would a PS3 emulator run on but a PS4? Likewise, for PSP games on a PSP2.
However, as the article points out, it would be a shock if Sony was not planning well in advance for its next-generation console. Moreover, it's abundantly clear that the development hardware for a PS4 simply doesn't exist yet.
Bring back the old stuff
Most likely, Sony is looking to enable its current platforms to play older games - more backwards compatibility, if you will. Homebrewers already know the PSP can play whatever they feel like putting on it, while the original 60GB PS3 had hardware support for PS2 games.