Sigh.
For the record, all PS3s made prior to the 80 gig and a few early models of the 80 gig had full (or close to full) backwards compatibility with the PS2. My late-model 80 gig, the 40 gig, and every single PS3 Slim can't play any PS2 games.
They did it to reduce the sticker price in order to compete with the cheaper (basic model) 360s.