Erio, I got the 93% because it's not just the price of the game, it's the price of the two subsequent expansions on their release as well. If you'd bought each as it came out, you'd have basically bought 3 games... which you're now getting for $9.99.
a) it's included in the installer, so they would have to compile one every time someone buys a game
Or just include another setup file with the unique key in it which is generated on-the-fly from the cd key stored with the account in the GoG database and tell the setup to use that for the key and do whatever operations are needed to "install" that key.
Technologically, exactly what is being suggested (including the users key within the download files) is perfectly possible and not even that hard to do.
Technologically? No. Contractually? Might be harder than you think. Having dealt with these sorts of people before, I'm betting that what is going on behind the scenes is that GOG is having to request additional valid multiplayer keys from Atari/Infogrames... either every so often in batches, or (as wouldn't surprise me, when it comes to DRM convenience isn't even a factor compared to the publisher's right to protect and police its Intellectual Property) even possibly having to request a single key each time from them on a case by case basis, perhaps even having to submit proof of transaction each and every time.
I'm not saying I know this to be the case, I'm just saying having had to deal with such situations in the past, it could be a very plausible (and common) explanation for the delays.
This could also cause the greater delays in europe, as the licensing agreements for games, publishers and distributors are often completely different in europe than they are in the US... in fact, GOG might even have to contact a someone in a completely different department or office of the publisher, who might be dragging his feet. Lord help you all if that office is in France.
As piracy proves, you can do ANYTHING "technologically" with software. The technology isn't usually the barrier, rather it's the bureaucracy. The contracts, the lawyers, the red tape, and of course the publishers who say "you don't even get to smell the box of the game unless we get paid, and we'd rather inconvenience and infuriate the customer base than risk missing out on our cut." That is, after all, the entire spirit behind the very founding concept of DRM.