Strange! I never had any problem besides the slow connection with GG. (I have 25 games + a bunch of DLCs so far on there)… and the ones I've had trouble with are/were Direct2Drive. Didn't buy anything since Gamefly took over, but bought 3 games there and had trouble with 2 of the product keys/activation in the past.

I just shop around for the best deal between Steam, GMG and GG usually. Though I'll get things on GoG if at all possible normally.