I'm not in the industry, but I've asked a lot of questions over my 35 years of investing with brokers, Ameritrade and E-trade. I can't help you with what's happened to the various ECN's you mentioned. You're correct that NASD is a primary retail trading hub as I understand it.
Jeremy, I have heard numerous times that two years from now they will try to change how the trading gets done and eventually it will be all electronically..Is there a truth to this or have you heard anything about it?? I heard that theres lot of advantages by doing this..