Some patches are platform centric.
(reading the Dev Log)
For instance, v 1.1.15 fixed an error concerning Steam cloud syncing from v 1.1.14. There's no reason why we would get a patch like that right away. On the other hand, when modding was brought in and there was the error with the in-game way to install mods from zips (1.1.00 if I remember correctly,) we got that while the Steam version was still running 1.0.99 because it didn't really effect them that much since they had the workshop, and that was really the only place to get them at the time.
Plus, he can just go ahead and throw a patch up on Steam. Here, it goes through the GOG team first if I'm not mistaken as they update the patches/full builds to make them available. Also, Steam has a nice setup for dev's beta testing patches that don't effect the main builds that everyone else is playing.
I believe in Defender's Quest's case, we are on the same major release. I think he's working through some other translations right now, but as soon as those are done; I'm sure the new build/patch will be sent here.
Usually I find the lag behind Steam patches to those here are minimal (I'm referring to other games as well here,) and a lot of those Steam-only version patches effect features only on Steam i.e cloud syncing, Steam achievements...
EDIT: As of now, the Steam public version is 1.1.33. I don't see any real differences between that one and GOG's current version. It's still just English, German & Czech.
Post edited January 29, 2014 by babaganoosh13