More than anything else, the bachelor's degree seems to be a pass to a social class. Want a white collar job? Get a four year degree. Any four-year degree will do for most of them, as it will mark you as part of the educated middle class.
I can't count how many times I've heard it repeated that what major you had in college matters very little in the corporate world - or how many times I've heard someone say that what they majored in had nothing to do with what they do now. There's even a certain measure of truth to claims that the bachelor's degree is diluted, because there are very few specific things you need to know on graduation. Pick the right school, the right major, the right classes, and the right teachers, and you may coast through having learned very little curriculum material.
It does mark a measure of persistence, and work, or at least financial support of some kind, but while having a degree with (say) a major in chemistry means something specific, the bachelor's degree in general seems to be more a social marking than an educational one. And that, ladies and gentlemen, is why demand for a college education is and will remain sky-high - because here in America, it's a pass into the white collar class. Those with a four year degree seem to bear some kind of warrant to look down upon those without one.
Mere curriculum material, I wager, would not warrant such demand. But social standing? Social standing is priceless, and I suspect that, more than anything else, accounts for the disparity in pay grade between those with and those without the sheepskin.