The one exception to this is that a key for multiplayer access in mostly single player games is sometimes not included in the DRM definition. GOG has a number of games with codes needed for online access via central server; this is needed to be able to ban players for abuse and is still technically DRM but I personally consider it different type of thing when the game is primarily offline. Best is when there are multiplayer alternatives to the central server that don't require a key but that is fairly rare. Personally I don't use multiplayer anyway.
All in all, the experience from GOG is much more customer friendly than other game stores (there are only a few other tiny stores that I know about that are DRM-free and don't require their client to be able to buy and/or download games). They aren't perfect but you can download the installer directly from the website if you want or use a client if you want. Games work fully offline with no code needed. You can refund a game for essentially any reason within 30 days even if you have downloaded and played the game (there is some unspecified limit to number of refunds but it isn't tiny if you are just refunding a few you don't like). I'm not 100% certain but I'm fairly sure they don't ever remove inactive accounts.
Unfortunately, the value of DRM-free is often reduced somewhat by the "release a buggy mess and if it sells well enough fix it eventually" philosophy that most developers have these days. Not having access to updates can worst case make the game unplayable and often makes it less pleasant (of course, there are also cases where updates make it worse :/). So DRM-free isn't a complete solution for not being able to access an account, but at least once you have played a game you can play the same version again even if you can't access your account.
There was never a time when the definition of DRM didn't include license key checks.