Well over a year ago after continually pressing Scottrade for an answer to their SIVC ban I got some lame excuse from them but it's been so long I don't remember what I was told. All I remember is that their excuse was lame.
Back then someone suggested a plausible explanation for Scottrade - that NITE is short SIVC and the NITE head honcho is buddies with the Scottrade head honcho. They sit on each other's boards or something like that.
I've got my SIVC in IB, zecco, and (hah, hah, hah) Scottrade after ACATing my Roth IRA from IB to Scottrade.