Actually it did have to do with talent. His main problems aside from attitude are he drops far too many easy passes(although he's been better with that this year), and his route running is terrible. The route will call for him to do a curl-in, and he'll do a curl-out, then go bitch on the sidelines about not getting the ball.
Parcells was just tired of dealing with a guy who has a #1 WR's mouth in a #3 WR's body.