One word: Money. Degrees aren't created equal. My brother is an educated man with a masters in his field, but all from state U. His daughter went to an Ivy League school, and only has a BA. At 34 she was already a VP in a multinational. In his own words, "She lives a lifestyle that I could never afford to become accustomed to."
I didn't read it online, so I probably doesn't count, but the WSJ did a study and found that Ivy League grads could expect to earn close to 50% more in their lifetimes than those with comparable degrees from state universities.
That does make sense... but if someone is smart enough to go to an Ivy League school then there is certainly going to be some financial aid in the cards that would make such an education affordable. If someone has to pay full MSRP for an Ivy League education, that person probably does not belong there in the first place.
That being said, while Ivy League grads may have it in the cards to earn more, that doesn't mean that a person with drive and ambition who lacks a degree or who has a degree from a "lesser" school is relegated to a life of not making a good amount of money, either.