After seeing numerous offhand refernces to this "MacroQuest" thing, I went and looked it up, and realized that it was (duh) the program I'd been hearing about that allowed people to make tons of plat from automated tradeskill combines.
It also appears that SoE removed a lot, if not all, of the profitable combines in the same patch (10/31?) that broke SEQ.
Since the tradeskill exploitation actually warranted an in-game warning message, is it possible that the whole MacroQuest thing just pissed them off enough that they decided to take a more hard-line stand against ALL 3rd-party programs, including SEQ?