Someone else might be more useful, but I seem to recall I used to have CoH installed via the steam client and they used to sell it in their store back before it went F2P at any rate (possibly during the days of the old CoH launcher, rather than the NCSoft one...).
/this
the architect version and GR versions were both sold on steam and i actually DL'd the game through steam, it was taken off of steam when the game switched launchers and when it went f2p
it would be nice to see it on steam again, however i have heard that in order to get on the steam greenlight you actually have to pay valve money
im not saying this route is not an option, but if valve decides to try to buy coh then it will be on steam anyway if they get it