I have only 3 games so I decided to get more opinions about update policy at GOG.

Kingdom
The developer release the updates on steam first. After some days they are released on GOG. While it is ok for a single player game like Kingdom, I see a problem with multiplayer games.

Hammerwatch
The windows version is missing the last update that makes cross platform multiplayer very unstable. The Linux version is far behind and can not be used for multiplayer.

Is this update policy a general problem on GOG or are there just a few games?

Gog is slower at updating their catalog than Steam is. It took some time for Gog to get the most recent version of Rise of the Triad.

The problem is not on GOG's side but the developer's, they are the ones sending in their updates to GOG.

On Steam the updates are managed by the developers, on Gog by the Gog staff. It usually takes them a few working days to upload a patch after they've got it from the devs. Be it because they do additional testing, or they have a backlog of past work, or whatever other reason.

Sometimes they don't get the updates at all, and that's the publisher\developer being an ass.

The bottom line is that GOG's not really the best option at the moment when it comes to online gaming. Best option for single player, but online's not really there yet, no.