Heh. If they won't tell DEF, maybe the real answer isn't forthcoming soon, so I'll throw in my two cents of speculation 
Lacking evidence to the contrary, I'd believe that the NYSE quotes come from the NYSE itself. I've watched them against other quote vendors and they are always the fastest. It routinely beats myTrack (who gets quotes from S&P), for example, by over a second.
Now, if we could just get IB to show those opening indications in NYSE stocks like they used to...
I have evidence that Instinet, Island, REDIBook, and ARCA are all coming from those individual ECNs, too.
I have no experience regarding the NASDAQ feed(s).

Lacking evidence to the contrary, I'd believe that the NYSE quotes come from the NYSE itself. I've watched them against other quote vendors and they are always the fastest. It routinely beats myTrack (who gets quotes from S&P), for example, by over a second.
Now, if we could just get IB to show those opening indications in NYSE stocks like they used to...
I have evidence that Instinet, Island, REDIBook, and ARCA are all coming from those individual ECNs, too.
I have no experience regarding the NASDAQ feed(s).