How come my PS3 can't play PS2 games?

I don't know what's wrong with it, I got the PS3 yesterday, and the game that currently isn't working is Madden '08. In the PS3 manual, it says that you CAN'T play PS2 games, but from other sources, I think I should be able to.

Help is appreciated.
Update: Could you add GB to it?
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