Sounds right on, but your understanding is more in depth than mine on the listed side. AMEX uses some kind of combo of live/electronic order execution that I have not bothered to educate myself on. I do believe we are seeing the end of the live auction, AMEX, NYSE, CBOE and NYMEX are the last of them. NYMEX resisted for a long time but my buddy trades crude oil and he has been saying recently how much of the order flow is now coming through electronically in that market as well.
When I was a trader, most of my trading was on NSDQ. Order execution has changed a great deal since my time a few years ago. MM's used to actually post there a true order, now you see them post a 100 shares and refresh for 100m.