Why Do Employers Require College Degrees That Aren't Necessary?

Slashdot reader pefisher writes:
A lot of us on Slashdot have noticed that potential employers advertise for things they don't need. To the point that sometimes they even ask for things that don't exist. Like asking for ten years of experience in a technology that has only just been introduced. It's frustrating because it makes you wonder "what's this employers real game?"
Do they just want to say they advertised for the position, or are they really so immensely stupid, so disconnected from thei