I whole heartedly agree. Not only that but I have emailed ludeon asking about gog and voted on the gog forums for them to try to get rimworld.
In case any one is curious why. It is because although I do like many of the services steam offers they do no let you choose to prevent a game from updating, only to not update until game launch. It use to be a common myth that stop auto update meant it would not update even at launch but they have changed this to actually say do not update until launch.
Yes of course I could buy a drm free version straight from ludeon studios, but gog not only holds a library of games for me that I can redownload when I need to just like steam, they are also have an optional steam like client now. Key word being optional, still drm free and no forced updates.
At the moment I am aware that on steam you can choose in the beta menu to go back to a earlier patch but that is only if a developer allows the option and only after first allowing the update to download and then going into the menu and finding the patch you were on.
It is much easier for me to deal with keeping my save game and using mods on non steam versions and much more reliable. gog simply offers many of the benefits of steam but without losing the benefits of drm free.
I promise you this, if rimworld comes to gog I will buy no less then two more copies and possibly more for me and my family, through gog.com
tldr: I prefer to get all my games through gog now and would love to see rimworld for sale through gog.com and there are many reasons why besides drm free.