According to Joystiq.com:
Apparently Sony wants to offer a cheap, non-Value Pack version of the the Playstation Portable. The non-Value “standalone” pack will exclude the PSP soft-case and the Spider-Man 2 UMD. The PSP was expected to be sold out at launch; however, it did not. So lowering the price is probably a wise idea to push more sales. The expected retail price will be $200.