It seems Rockstar wants to get you excited with the Grand Theft Auto franchise before eventually releasing the much anticipated GTA V title.
Just recently, Grand Theft Auto 3 and Grand Theft Auto: Vice City has been rolled into the Entertainment Software Rating Board (ESRB) for their rating system which puts a real indication that the classic titles is totally PSN-bound.
So as to put ourselves clearly, the games will be ported to the PlayStation 3 and marketed for the PlayStation Store. Both GTA 3 and Vice City were big titles for the PS2 back when they released so it does makes sense that Sony would want them available online for the PS3 consumers.
However, there has been no confirmation from neither Rockstar Games nor Sony, but ESRB is an extremely reliable bet when it comes to re-releases especially for a huge franchise like Grand Theft Auto.