Originally Posted by Someone from Sony
We have made clear on many occasions that our priority is on developing innovative new features and services for PS3 and not on backwards compatibility. The 40GB model no longer contains any elements of the PS2 chip set which powered backwards compatibility in previous models, and is therefore only compatible with PS one titles
So it is backwards compatible with PS1, not PS2.
Edit: if you trust people from Sony to know what they're talking about that is...