CS, i don't think you can compare things like that unless your buying the same or very similar condos in the same building. there's so many variables to consider like the property itself, buyers interest in the property, owner's need to sell, etc. just because you got $80K off your deal doesn't mean it was all due to the realtor. if your offer was the only one on the table and there hadn't been any action for a while maybe the owner was just up against a wall and needed to sell.
Completely agree that it's not apples to apples. But to generalize that using a realtor is ripping yourself off, or focusing in on the commission to the exclusion of all the other variables is equally naive. There's no question in my mind that in my situation, I saved more by using a realtor then I would have by trying to go it on my own. YMMV.