Remember the Quake 1 "demo" (shareware) that contained an entire chapter out of the 4+1 chapters available in the full game? Nowadays game demos contain 5 minutes of gameplay and 15 minutes of cutscenes....if there's a demo at all.
Oh, and if you want a nice read about id software and the time of Doom and Quake, I suggest you pick up Masters of Doom. It's a light read and shows you what happened behind the scenes during those times.