a PC game me and my bro could always install on two computers buying one copy
If you are trying to play a single player game on multiple computers at the same time, you can do that with offline mode. I did this to play Bioshock 2 on my friend's account. You lose all the Steam Friends, Achievements, Cloud saves, Community, etc., but that's the trade you make.
For online games, historically, you always needed separate CD keys anyways, so nothing changes there.
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_foolmo_
'Most people at least try to say something funny. See foolmo's post as an example.' - The Real Truth