Well, as much as people within the Bills fan base scoff at the prospect of Jeff Tuel starting, the front office signed him for a reason.
He and EJ were both rookies last year, they were bound to play within themselves, over think in situations that they would typically rely on instincts. There is a lot of pressure to win football games in the NFL. They aren't playing football for fun anymore. This is their career, not just their passion. I think the gravity of that situation, the pressure to not only be successful for yourself or your team, but to be successful for your family and your future is a lot to wrap your head around when you first come into the league.
I personally feel EJ will improve this year, but IF he doesn't I would expect the Bills to turn to their other investment of the 2013 draft.