That's not correct. While PC games used CD keys for a long time before, those keys were only checked during the installation and only offline therefore weren't used up and you could lend the game to a friend without any problems or even rent it from stores. When I was young lending PC games between friends was very common and at least in my country video rental shop usually had PC and console games for rental as well.I don't know why people are comparing Steam to this.
Since the NES/Mastersystem I've been able to rent games for each generation of console up until current gen.
PC has had DRM and cdkeys for a long long time and historically you've never been able to rent or lend PC games that have keys and Steam is just an extension of this.
That games have to be activated online and tied to an account is still a relatively new thing and only happened to be the standard ~ 3-4 years ago. For example Fallout 3, the first Assassin's Creed or Sims 3 were still without any online activation but around that time it got more and more common for games to use some kind of DRM-system.