http://pcgamingwiki.com/wiki/The_Big_List_of_3rd_Party_DRM_on_Steam

The Steam versions of both Bioshock 1 and Bioshock 2 had their third party DRM removed. I don't know if they are DRM free as the Steam client may or may not be needed, I've not checked, but for me personally, I'm okay with Steam itself.

That's fine, but we're talking about the reasons why T2 isn't on GOG, and for that matter, it's not important whether the DRM is SecuRom or Steamworks and whether one is okay with certain types of DRM or not, because GOG isn't and the games are still not sold DRM-free online, although T2 would have the opportunity to do it (I checked the UK site for Bioshock on GamersGate and it says SecuRom, not DRM free). And when I run the Steam version of Bioshock.exe, it tries to connect with my Steam account.

Steam CEG is still DRM though, and I can tell you that Bioahock 2 at the very least is CEG protected.

Bioshock 1 was one of my absolute favorite games! I only got a chance to play it on a console, but I would much rather play it on PC. But I have a feeling it will be a very long time before GOG can get anything from the Bioshock series.

Yes, and I daresay both use Steam as DRM. I've a feeling the first game just uses the Steam 'stub' DRM (CEG) meaning that the user must own the game on Steam and requires the client to be running. The second game might be full Steamworks DRM. But the main thing is that the rubbish 3rd party DRM schemes (SecuROM and GFWL) have been removed, and that's what allowed me to finally buy the games on Steam as there was no way either SecuROM or GFWL was ever going to get onto my PC.