He was 11-5 last year and won a playoff game, better than his predecessor (although I thought firing Marty was a bad idea). Who cares if he went 11-5 vs. 14-2.... the Giants went 10-6 and won the Super Bowl (and for the Eagles fans this year, I don't think they could care that they went 9-6-1). The team this year didn't start well, but they were without a healthy LDT and their best defensive player in Merriman. 4 of their 8 losses were to teams that made the playoffs, a 5th was to 11 win New England, and a 6th was the highway robbery game against Denver. 6 of their losses were by a total of 17 points (including 2 by 1 point, 1 by 2 points, and 1 by 3 points). If you look at their expected W/L record, based on points scored and allowed, they should have been 10-6. Of course, that's where luck factors in... something they had very little of.
I'm no Norv apologist, I think he was horrible in DC and was given the reins to an awful team in Oakland, but in 2 years with SD he's made the playoffs twice and won 2 playoff games (Marty won 0 in 4 years) making the 2nd round both times. If he has a losing season next year then I'd fire him, but right now he's playing with house money.