Attitude counts. I'm not saying that Al Davis isn't an idiot, but it's easy to see how a normal NFL GM might look around the league at WRs like Terrell Owens, Chad Johnson, Anquan Boldin, etc., and think, "You know, I need a WR. I can either take Crabtree, who's earned a reputation as a bit of a prima donna already, or I can take a guy who projects to be 90 percent as good and isn't going to be a princess. Screw it; I'll take a chance on the guy who's not going to poison my locker room."
Given that it's Davis, that probably wasn't his thinking, but you can see why somebody wouldn't have to be insane to take Heyward-Bey over Crabtree.