I don't know why you would say that. He's not getting it because he only had 2 weeks to learn it, and was switched to corner in the preseason because of injuries. Saban said it himself that it is hard to learn what he needs to during the regular season because everyweek they are game planning for the next opponent.
Jason Allen I believe graduated from School early, and I have heard an interview where he has said he wants to go into law after his football career is over. That doesn't sound like someone that's not smart enough to learn the system.
http://www.nfl.com/draft/profiles/2006/allen_jason
Here is a quote from the above article to support what i'm saying.
MENTAL ALERTNESSSection Grade: 5.5Allen is no doubt a smart young man when you consider that he has already graduated from Tennessee,