Latin vomitorium also referred to an emetic and vomere meant to vomit (and indeed is the source of our English word, via French); the figurative idea of an audience suddenly and violently issuing forth at the end of a performance gave rise to its application to an exit.
Quinion does not dispute the allegation that some wealthy romans used emetics as intermezzi between courses, (And why would he? There is no reason to believe that bulimia was invented by modern anxiety ridden actors, is there?) only that when the word was used by ancient writers in reference to a place or structure it referred to a passage in a theater and not a room in a home.
So why did I write that this bit of knowledge was a lucky break? Well, because now I'll have to look for another nutty story with which to regale the kids when I want to make the point that Roman had a very sophisticated civilization. In other words, I'll have to expand my repertoire of disgusting historical factoids. And that's called intellectual growth baby!
World Wide Words: Vomitorium
Google Scholar Hits for "vomitorium"
Apparently I'm a little late to the game on this. There's lots of paper on the misuse of the word by dummies like myself. What-ever.