Hmmm...
Well, that's a fair assumption.
Perhaps the best option would be for a situation wich happened with a few of the free games that GOG already has, though those are assumably free as they are genuinely abandonware. WC 1 and 2 are however, tiny in respect to filesize, even with their expansions. Thus, given that WC 1, 2, etc., are genuinely abandonware, bundle them up as a package and offer them as a free download. Free is a great way of winning your user base as well.
Speaking of which, I have to say that you'll likely never see the C&C old games on GOG, as although TD and TS are officially freeware/abandonware, they take up A LOT of space, each one in excess of a GB. That's a lot to give away for free without turning a profit.