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.

That doesn't invalidate your other point.

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.