All of the games on that list work without any kind of phone-home security check, or unlock code, or anything like that.

You didn't scroll down the linked forum post, did you?

• DEFCON - Linux: Game contacts a key verification server as described here. Win and Mac have offline executables that skip the verification. But under Linux there is no DRM-free offline executable.

• F.E.A.R. - arguably a bug that stays unfixed. Securom remnants weren't removed and can cause the single player game not to start.

That's pretty DRM-y.