When they talk about regression to the mean, they're talking about the tendency for any statistic to move towards the norm over time. In other words, if you flip a coin 100 times, the statistics say it's gonna come up heads just about 50 times. Now let's say you start flipping that coin and it comes up heads 15 out of the first 20 tries. Will that trend continue? No. "Regression to the mean" simply says that by the time you get to 100 coin flips, the ratio will settle down and you'll end up with something much closer to 1:1.
Football Outsiders makes some valid points when they say that the 49ers are unlikely to maintain their anomalous advantage in turnover differential, low rate of injury, and victory in close contests. True enough, but that doesn't mean they'll necessarily lose more games. With better production in the red zone, improvement on third down, more explosive plays, and higher point production, they might win MORE games this year. If statistics could accurately predict what was going to happen next, there would be no need to play the games. Truth is, anything can happen... and probably will.
My personal take is that it's gonna be much harder this year. A tougher schedule, we're the hunted instead of the hunter, and we'll probably have more turnovers and injuries. Balancing that, I see potentially large gains in Offensive production, and a relatively weak division. My prediction is that we'll go 9-7, but we'll be much better equipped to make a run in the playoffs. And my prediction has exactly the same chance as the stats-crunchers at FO.