Sony can (potentially) release the PSP2 at $500 because it is (rumored to be) so powerful that not making it a computer as well would be foolish.
I know I've said this like a hundred times, but, the PSP2 will be a tablet, or at least marketed as such. An at least 5" touchscreen, touchpad on the back, serious horsepower (for 1080p movies, multitasking, rendering DNA strands, etc.) and gaming controls make it a unique tablet in what is soon to be a very saturated market.
If I were Sony I'd also include calling because the assumed $300 price difference would be enough to separate it from the PSPhone's market, but that is unlikely, especially in the U.S where the Galaxy Tab had its calling abilities removed at the request of wireless carriers who are subsidizing it (where's the Consumer Protection Agency when you need it?).
Tablets are the hot new thing right now, and combining it with the nearly failed PSP makes a lot of sense to boost the viability of both. There are a lot of people out there who prefer a one handed tablet to the iPad because it increases usability; you can use it more easily when walking (dangerous, yes, but still...) or when seated but not at a table.
Personally, I'm waiting for HTC to announce their tablet which is rumored to have a 7" screen and dual core Tegra 2 (and keeping my fingers crossed that it'll make calls) but I'm also interested in the potential of a PSPTablet (PSPT? PST? PS(P)Tab?) because of the gaming aspect.
It is FAR too early to say the PSP2 is going to fail. Nintendo went after non-gamers with the DS and Wii, now Sony is looking to satisfy the tech geeks that are becoming more and more common as tech gets "cooler" and more mainstream with the PSPhone and tablet, that really may do everything.