When Thomas was with the Ravens he would line up almost anywhere on the field, with the exception of DT or CB. Belichick absolutely loves that kind of versatility and that is why he wanted to sign him as a free agent. The Ravens played a much more agressive defense then, which resulted in more sacks. Fans assumed and expected the same type of play from Thomas once he came here as a Patriot.
But the Pats coaching staff has felt compelled to play a more passive defense than what the Ravens employed the last two years due to the rest of the personnel on the field, and possibly due to the way some penalties are called now as well. Their decision to go with a bend-but-don't-break philosophy is due to their belief that the risk of giving up big plays to the opponent was not worth the potential reward of the big play (sack, turnover) by the defense.
Fans naturally yearn for that big play, so when they don't get it they point fingers at pass rushers for lack of sacks and corners for lack of interceptions on defense, as well as receivers and the quarterback for lack of touchdowns on offense. It's a natural reaction fueled by espn's highlight clips that include all the other team's big plays. Watch an hour of that and you walk away thinking every other team makes big plays all game long; you want the Patriots to have the big sack, the big interception, and the big touchdown of the day every week. And after a loss that becomes amplified to a point of 'we lost because this guy didn't make a highlight play' finger pointing.
Now has Adalius Thomas lost a half step? Maybe, I don't know. But in my opinion the biggest problem is that fan expectations are not in sync with the team's current defensive philosophy.
