Within the Android 2.3 Gingerbread software development kit are references to buttons common to gaming systems, like L1, L2, R1 and R2. They have a video at the site too if you want more info on it.
It is a good thing Sony is headed down this path. The PSP has been a very popular device but is several years old. The PSP2 has been talked about for a while now and it is still getting talked about, but not in a good way. Much of the talk is about the device being dead on arrival.
According to an article at Industry Gamers, kids are happy playing games on their iPod Touch and see little need for a dedicated gaming system. The software for portable gaming systems is more expensive, and there are fewer titles available as well. Paying a few dollars for a game is more appealing to most than paying $20-$30, even if the latter is a better game. For the same money, you can get a dozen enjoyable games
The other advantage to getting a smartphone is the gaming capabilities are free. You need the phone anyway for voice, texting and location based services. There is no need to spend over $100 for a dedicated gaming system. You also don't have to take two devices with you. The smartphone does it all.
There may be one more wave of portable gaming systems, but it remains to be seen how well they do in the market after the diehard fans scoop one up. It is a pretty sure thing though that this wave will be it. They just can't compete with the overall value a smartphone offers.