According to this article, there is a growing list of problem games that may not allow for the Sony Playstation 3 to be 100% backwards compatible.

SCEI has published a list of nine PlayStation 2 games and 38 PlayStation games that run into problems on the new console. The SCPH-75000 will be available in Japan from Nov. 23, and is modeled on the slim-line PlayStation 2 that SCEI put on sale just under a year ago. In launching the new model, SCEI is using an oft-employed sales-boosting tactic of making a console available in a different color — silver in this case — for a limited period.