You're probably right, JAX is a better NFL D/ST than in FF.
They don't seem to score on turnovers or kick returns very often, etc. That stuff tends to be 'lucky', so you never know. Mathis is one of the better CBs in the league and thier D line is very good. Playing Manning x2 a year probably doesn't help since he's not offering up many pick 6's anymore. Maybe Schaub will help the cause tomorrow. If your league awards point for scoring allowed, they should continue to perform well w/ some TOs mixed in.
Also, the JAX offense is playing well (limited TOs and long drives w/ a good run game), so they're not on the field as much as MN, CHI, etc.
Similar to SD's D (last year more than now). Good winning games, but not great in FF. MDJ should take a KO or 2 for scores.