throgh: The developers seem to have abandoned the game in its current state here and yes: Take it from the catalogue at all. There is no need for this. Ah and by the way:
Age of Wonders 3 should be also removed, same reason here.
tremere110: Aow 3 has the current stable steam patch and all the DLCs. It's missing the beta patch which is only a week old. I wouldn't call that abandoned. Was there an announcement to that effect?
Age of Wonders 3 will not get the native version for Linux which is available exclusive over Steam and the developers said, that they are not able or willing to invest work in a DRM-free built. Linux-customers are therefore left alone! The developers for
Armello have done this now for their complete game: Okay it will get updates but no more content because they want use Steamworks instead trusting the customers. And there are more examples here also on GOG for games where the developers or Studios or even GOG itself left the users completely alone.