Look at draftbreakdown.com. Pull up Sam against the better teams. He'll be single blocked and won't be much of a factor. But he ripped up Ark and Ark State.
He's just not quick enough. And he won't be a special teams player because of that.
I won't get into a Tebow argument but he gives teams a better chance to win that many of the clipboard holders in the NFL. Thing is, they're cheaper and no one is clamoring for Matt McGloin or Tavaris Jackson to get into the game.