PaterAlf: I'm not even sure the quoted Tinybuild employee knew what he was talking about. Several of their games on GOG are up-to-date, some even have their soundtracks and art books here. So it doesn't seem to be an official company policy.
It might be a shitty thing that some of their games are outdated, but I don't see a reason to boycott them as a whole.
Lord_Kane: Peter if you can get me conclusive proof ( I dont own any tinybuild games) I will happily shut it down.
Pathologic 2: GOG = 1.4.25127
Steam = 1.4.25127
Artbook and Soundtrack DLC are on GOG as well.
Graveyard Keeper: GOG = 1.124
Steam = 1.124
Artbook, Soundtrack and Collector's Edition (including both) aren't on GOG though.
Clustertruck: Can't find the exact version number on Steam, but looking at the changelogs, the game should be up-to-date.
It is missing the level editor and the soundtrack DLC though.
Swag and Sorcery: GOG = 1.030
Steam = 1.030
Lovely Planet: I don't know about this one.
Hello Neighbor: GOG = 1.2
Steam = 1.3
Game is indeed outdate and missing soundtrack DLCs and Collector's Edition.
Phantom Trigger: Not sure about this one. It got an update on Steam on release day. Might already be included in the GOG release. The soundtrack DLC is missing though.
The Final Station: Can't find the exact version numbers, but judging from the changelogs the game should be up-to-date. DLCs are on GOG as well.
Punch Club: It was outdated for years, but it got an update some weeks ago. It's up-to-date now. Deluxe Edition and Upgrade path are on GOG as well.
Party Hard: It's outdated and missing DLCs.
Party Hard 2: Outdated and missing DLCs.
So it's a mixed bag (and I certainly won't praise them for being an awesome publisher), but as far as I can see only the Party Hard games and Hello Neighbor are really outdated.