Shots against is not really that telling a stat, it's the quality of the chances.
Since winning the cup we have lost Mitchell, Regehr and Voynov and replaced them with Ehrhoff, Forbort and McNabb. That is a massive drop off. Thankfully we have the talent up front to make up for the defensive shortcomings.
That's absolutely a huge drop in talent there. Thing is, the Kings just don't allow a whole lot of chances. First in shots against and 4th in goals allowed means most of those chances are not that good.
Our current D system doesn't really need talent, it just needs guys that understand how to play it. On the defensive side, I doubt there is much of a dropoff at all. Now points from the blue-line, that's another story and something I'm more worried about.