In the DVD industry, this kind of practice is called "double dipping" and it absolutely sucks. It makes people that have purchased the original feel neglected and the real fans are punished because in order to access the new content, you have to repurchase a new copy. While the practice is considered fine when there's some amount of transparency, Rockstar has been handling it all wrong. Don't call a game a PSP-exclusive if it'll head to another system immediately. Don't consider the games equal, when they're not. Shouldn't gamers have a choice to get the best version of GTA possible?
According to GTAPortable.com, the Italian Take-Two website refers to Vice City Stories on PS2 as having better graphics and exclusive, unpublished content. Hopefully, it won't make PSP gamers feel like the $50 they spent on the original went wasted.