Psyringe: I do a bit of support work for GamersGate, so I can see that there are different regional versions of the game in the database, and I see tickets coming in from e.g. EU customers who bought the game through a US proxy and who report that Steam rejects their key.
(Side note: I occasionally mention my "affiliation" with GamersGate since I don't want to conceal it; on the other hand I really enjoy GOG as a place where I can be myself, and not "the guy who does stuff for GamersGate". Therefore I usually keep my work for GamersGate, and my activities as a community member here, strictly separate. However, sometimes it makes sense to make an exception, for example when a bit of information can prevent someone from buying a key that they might not be able to use.)
Thank you for the clarification. Your avatar on GOG reminds me of the "work" I do, and I keep that strictly separate from GOG too :)