Crosmando: It's a different audience.
Pheace: That said, there's no reason to believe that among Steam subscribers there aren't plenty of people who enjoy oldies as well. Unless you feel enjoying oldies has to go hand in hand with enjoying DRM-free (which would make the oldie fanbase more exclusive to GOG)
I don't doubt these games sold more there than here, based on the larger install base alone, but I'm willing to bet it was mostly due impulse purchases, people who saw it on the front page one day and said "what the hell, I'll try it", or if they played it before, felt they were up for the nostalgia trip; and not because there is a dedicated fanbase for old games on Steam, eagerly anticipating the next release by Night Dive or someone else.
The oldie fanbase is indeed more exclusive to GOG, for the simple fact that it appeals to their tastes more. Just like there may be DRM-free games on Steam, but there's better places to find that, there are better places to find oldies, even if Steam does carry some.
My point is he's right to say it's a different audience.