I remember reading a paper or something about games of chance, and how people square randomness with reward. The gist of it was that people don't necessarily want random results; they want good results that feel random. They are trying to capture the feeling that a higher power, the universe, the Fates, whatever, is smiling upon them personally.
That's why rolling up stats and getting an 18 feels so much better than point-buying an 18, or selecting an 18 from an array. It's still the same 18, but how you came to get that 18 matters. It can make a big difference for some folks.