Semi-interesting fact (I don't own a PS2 so, i didn't know this)

This trend - started by Sony with the PS2, as backwards compatibility in home consoles was certainly not the norm before then - is set to continue with the PS3, which will offer emulation for the PS2 and hence for the PSone.

"PSone runs on the PlayStation 2 through emulation rather than actual hardware. PlayStation 3 will offer the same compatibility for PS2 software and the format will continue forever,"

Microsoft should know this, as it (kinda) says that the Xbox 2 would not be easier to mod as a result of it being backwards compatible.

http://www.theregister.co.uk/2003/09/02/ps3_will_play_ps2_psone/