With my disc version I always needed DVD in the reader.
With Steam version I believe it should behave similarly to ME1 (thus Steam DRM)
With Origin version, though things are a bit different.
If you don't touch anything after installation and run directly the game executable (Origin can even be closed), a pop up comes out and ask you to log-in with your EA account (where I guess a ME2 license has to be registered).
After that %PROGRAMDATA%\Electronic Arts\EA Services\License\mass_effect_2_ce.dlf
is created (file name may differ between game localizations)
Then the game starts flawlessly forever with nothing in background.
Or you could start the game through Origin that should automate the process (I don't even think a normal person could notice that)
This is quite problematic since unexperienced people could report wrong information (like me before some brain work)
Anyway, I'm quite sure this can be called "Online activation".. but should that even be Account-based activation?
The description in the drm page is quite messy imo