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.
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.