I think the point of PS1 classics, is to increase the amount of content on the PSN, full games that are less that 700MB. (Atleast thats what they should be, I have no experience downloading them, but that was the storage limit of the PS1)
To put up PS2 games would require much more space and bandwidth. And would make it less profitable, in the current situation one must buy a PS2 if they do not already own one to play these games.








