Yeah, I has read some stuff bragging about the awd Tesla not having a center diff. And I could have sworn that long ago I read that the rear wheels were individually powered as well. Clearly I'm going insane.
Bottom line: I'm with JST. RWD + open diff + all season tires = stuck on any non-trivial incline. It sucks.
But speaking of LSD's, I was in a gravel lot the other day and did a controlled power slide with the rear. It was awesome. I can't wait to try it in the snow.