I think it’s pretty clear from context that they mean they have the ability to perpetually play the games because of the lack of DRM, not the right.

Plenty claim it's their right and with much ferocity while as vehemently ignoring that there are plenty of games on GOG that offer reduced content when playing offline (an extensive list was posted by someone). Also, because games on Steam must disclose their use of DRM (and anti-cheat), people can just buy DRM-free games which can be backed up just as well. Goldberg is a drop-in library for games that use Steam APIs. So everything is fine there as well for people who actually make informed buying decisions.