vicklemos: A lot of Steam accounts are there solely for the purpose of dumping keys from bundles.
Others who have 2500 games on their account literally glance at their "milestones" on a daily basis. These dudes won't play a tiny bit of their games while living on earth.
I find GOG accounts to be much more genuine, hard earned. An example? A guy I know personally who has 200+ titles in here and has very few on steam. He told me that "Steam has a lot of flashy propaganda, whilst GOG is surely a lot more about gaming".
That's really just stereotyping. I know collectors on Steam with 2500+ games who I'd bet play more games than most GOG users. I also know that a lot of people played hundreds (or more) of hours of Skyrim and other Steam titles. On the other hand, I'm sure that a lot of GOG users collect old games for old times sake and hardly get to play them.
I assume that there are a lot more serious gamers (or hardcore, or whatever you want to call people who play a lot of hours) on Steam than on GOG. Not averages, just absolute numbers.