I've been wondering that myself, and it only encourages immaturity on the parts of the adult children. I saw stark differences between those whose parents paid for school and those that did not when I was there.
Incidentally, in a number of states now (e.g. California) it is absolutely assumed that the parents will pay for school for the purposes of financial aid. The income and assets of your parents will be included in your own for the purposes of aid well into your 20s, whether or not you receive a dime from your parents. Which is pretty messed up, if you ask me.
Since when did it become "expected" that parents would put their children through college?
Inflation has made it virtually impossible for a young person to earn enough to complete college in a reasonable period without significant debt. When I finished my B.S. at a state university in 1977 I had less than $1000 in debt and had earned enough working summers to pay about half of the cost of my education (less than $3000 /yr); my parents paid the other half. My parents' contribution required some sacrifice on their part. They willingly 'did without' some things so I had more opportunity.
I have two children who both completed B.S. degrees at state universities two years ago. The annual cost for each was close to $14000. They did their best to earn as much as they could but didn't come close to paying half. We sacrificed to make sure they finished debt free. Both were told grad school was their responsibility.
The key message of this thread is that one's continued employability requires current job skills. Thomas Friedman's 'The World is Flat' should be required reading by all young people. Parents need to instill into their children a life long passion for learning. College and graduate degrees are no guarantee of employability, but can provide important fundamental skills.
BTW - we told both our kids that our financial support was contingent upon their prudent lifestyle choices. My wife and I made it clear that we were paying for performance. We were not about to make the required sacrifices just to have them goof off - and we made certain they understood that.