I'm going to get my head bitten off here and I don't know what happened for sure, I don't imagine any of us do.
In my opinion, SD had some good info to contribute, but he abused this board to the point where it was possibly easier for the mods to tell him to leave than it was to put up with watching this board spiral out of control almost every time he posted something. This is just in my opinion of course, I have no idea if what Ender said is really the case or not, I don't think any of us will know.
But there was a lot of controversey about him being here after the way he had treated a number of people. I believe there is room to screw up on this board, we are all human and most of us have done so (I KNOW I have). But there comes a point when one must whey the pros and cons and I think his cons finally outweighed the pros.
I'm not sure if he's gone of his own accord or was asked to leave, and really, I don't care. He has a way of causing drama even when he's not here. This board has been a lot calmer in the last few months.... again, JUST MY OPINION though.