Is that online activation Steam or is it a third party thing? Steam allows selling games that have external DRM like that. I think they, themselves, don't do it.
Steamworks, the integration library for games to interact with Steam features, has an optional DRM component. It's not a particularly impressive one, so it's more about stopping people copy/pasting their steamapps folder than stopping dedicated pirates, hence why so many publishers use alternative solutions.
But that's just using what you payed for, it only very slightly overlaps with what actually owning something entails.