Once again we have to do GOGs work.
What is GOG's work in this case?
At least GOG is probably not trying to track all GOG games, whether they receive any updates elsewhere. That would be quite an impossible task. Valve doesn't track either how games on their store are being updated elsewhere, and whether the Steam version receives all the same content and updates. And no one expects them to.
Now, if you people have informed GOG about some missing update, THEN I agree it kinda is on GOG's turf.
I inform GOG, GOG ignores me ... eof.
I have stopped to count how often the community brought updates here after GOG failed to do so (if they even tried which I doubt). The usual experience is as follows:
Support ticket: Game is not updated ... update on Steam from XYZ ... please fix.
GOG's reply: Thank you so much ... we have forwarded this to the right department and have closed your ticket.
Community does the same and sometimes they succeed.
Not once did I experience that GOG actually managed to get an update for an outdated game by themselves after I've told them that the game is outdated. So before you are defending them I'd suggest you to see for yourself how lazy GOG is managing tickets about missing updates.
Last missing update I informed GOG about was "Someday You'll Return" and as always they thanked me and managed to do exactly NOTHING! I even asked them again if they have some news after a few months and all I got as reply was that there are no news.
The way GOG is acting in case of missing updates is nothing more than a joke and should not be defended by anybody imo.