Hi there,
So, with the DRM-free builds (which is kind of a misnomer because none of our builds have any DRM, but still), there's not any form of in-game updater. That would require some binary diffing/patching capabilities that I just don't have right now, as well as costing hundreds of dollars a month in hosting charges if past games are anything to go by.
With both Steam and the GOG Galaxy client, they are tools that have inherent binary diffing as part of themselves, and they shoulder the costs of that rather than me having to pay for infrastructure on that myself. The GOG Galaxy client version and the Steam version are always updated at the exact same time, so there's no lag there.
For the "standalone" build that GOG creates for people to install, they have a semi-automated process for creating those, and they do them periodically after I've updated the game. I don't control when or how frequently they do that, and it involves a full download of the game and install of it. Really not something tenable for when there are multiple updates in a week in my opinion.
Both the Steam and GOG Galaxy clients are essentially "delivery mechanisms" for binary diffs for games. To avoid using them for a game of this scale (6GB or so) would require a lot of infrastructure as well as me to reinvent what they already invented. There's definitely nothing tying the game to either platform in terms of once you have the game downloaded it is on your machine for good and not something that can be removed or caused to not function due to lack of a network connection or what have you.
The unfortunate thing about the GOG Galaxy client on linux is that... it doesn't support linux yet. I'm not really sure what their timeframe is on this, but they sure have a lot of people asking for it and you can also add your own voices to that if you want:
https://www.gog.com/wishlist/galaxy/release_the_gog_galaxy_client_for_linuxHope that makes sense; the full installers should be up to date within a few days after the Steam and GOG Galaxy client updates go live, at worst, at any rate.
Best,
Chris