i thought all PS3's were backwards Compatible with PSX games via Software Emulation. (Including The Slim) Unless that means the ones you can get off the PSN for about a fiver to ten quid.
That's What They're Using but instead of the old one it's a new piece of software better written to take advantage of Both The Cell CPU and RSX GPU. as new models lack the Emotion Engine (A 299Mhz RISC CPU) And The Graphics Sythesizer that were used in the PS2. A Patent Was Filed For It in 2008. As They Plan To Kill PS2 Support In the Next Year Or So it's a quick profit to release all titles at reduced prices ala Xbox Live.