Is it fairly rare? I know a lot of upper middle class friends who's parents had 0 savings and could not help at all with college, but by income guidelines they were expected to contribute a lot.
I have no data on how rare it is. My anecdotes suggest that it's more a matter of how the family prioritizes and allocates the income they have. There is a very tight spot in the curve where you make a "good income" but your associated lifestyle expenses are such that all of that income is allocated before any is earmarked for college. I still view that as a choice, though.
Oh it's a choice.. but it is a choice of the parent screwing the kid.
College is one of the first real things you do as an adult. i.e. you may sign up for giant loans you owe the rest of your life. Silly that the kid is responsible for the loan side, but if he has irresponsible parents he gets no financial aid.
If the alternative was every kid got money just based on the parents saying they wouldn't pay, it would take me less than one clock cycle to conclude I wouldn't pay for my kids either...
Expand the "Costs" section and you can see that if your family income is less than $100K, you're probably going to pay a small fraction of $50K.