The X11 system had a few major upgrades in the last few years. Although a lot of it was driven by the likes of driver developers inside Intel (and generally needed to be done), they were still dropping features before they had replacements ready. I really liked how I could have :0.0 and :0.1 with the one dual-head card, but they did away with that trick.
After I filed a bug, I actually got to complain to one of the programmers. His response boiled down to "we took that feature away because we've rebuilt the whole subsystem that could do it; you can do something similar in a future version." I said that wasn't acceptable and I wanted that feature back. He didn't respond. AFAIK, it still hasn't returned.
I guess if I could be bothered, I could go see if the bug was still open...
Wade.