Also, I was able to run Guardians of Middle Earth DRM-free as well, but since it's a multiplayer game, it didn't get past the part where it was updating multiplayer stuff, so I didn't add it to the list. I do find this interesting, however, because so far, there have been a ton of WB games that have run without Steam: Batman: Arkham Asylum, Scribblenauts Unlimited, the Mortal Kombat Arcade Kollection, and now Guardians of Middle Earth.
As a personal request, is anyone here who has the Mortal Kombat Komplete Edition (the PC version of the 2011 game) or Injustice: Gods Among Us Ultimate Edition willing to try running them without Steam? I usually just rename the main Steam.exe, and if they still don't run, make a shortcut with -nosteam at the end of the Target field. If nothing runs, then they won't run without the client.
EDIT: Okay, so the Dreamcast Collection is NOT DRM-free; it's only Sonic Adventure DX. If you buy them ANYWHERE other than Steam, they are, in fact, DRM-free.