How can ps2 games work on a PS3?

Answer 1

They can't except on early PS3 models that needed the PS2 game titles to insure that the PS3 was marketable, because it was released with only a limited number of PS3 games. These PS3 models sold at a loss to Sony and the ability to play PS2 games was discontinued as soon as enough PS3 game titles were available. See related link.

While all PS2 games will fit into the slot for games it is because the PS3 can play CDs, DVDs, and Blu-ray discs and not because they can all play PS2 games. They can't

The PS3 games consoles with 4 USB ports are the only ones that will play PS2 games according to Sony. Sony did not design the other models to be able to play PS2 games and there are no updates, hardware, software, programs, ETC that you can purchase to allow a PS3 with only 2 USB ports to play PS2 games. It is not actually the number of ports that matters so much as it is a way to identify the PS3 consoles that can play PS2 games. Sony also claims that all PS3 models will play select PS1 games. see related link