Norv has no control over the roster. The 75 year old idiot running the organization into the ground calls all the shots. The Raiders kept 8 WRs because 4 of them are either currently injured or coming back from major injuries. They kept 7 CBs because Al Davis thinks he's discovered a new defense that doesn't need LBs (we currently have a grand total of 2 on our roster... the other ones are really defensive lineman or career special teamers).
But back to Teyo... He's actually a pretty good player. He's a tweener TE/WR, not physical enough to be a starting TE and not fast enough to be a starting WR. I think the thing that pissed the coaching staff off the most about him is that he never really put in the effort on special teams (again because he's not a very physical player)... I thought he outplayed the starting TE this summer, but I guess it didn't matter.