Even in-state schools run close to 20K when you factor in books and fees. Penn State's tuition is 10K, and room/board is 8K. Add in about 2K per year in books. You think a middle-class family has 20K per year extra to spend per child, over 80K for 4 years ?
You forgot to add in the subsidy paid by the taxpayers. State colleges aren't any cheaper than private colleges, they just send the bills along different routes.
The $8K a year is kind of misleading. Unless the kid lives at home (which, BTW, is an option for many students, too), he is going to be spending that much on room/board anyway. So, the 8K isn't an additional expense.
You think a middle-class family has 20K per year extra to spend per child, over 80K for 4 years ?
I'm assuming they've put something away during the first 18 years of their kids' life for a college fund. Even on the low end, assume they put away $1K per year for 18 years. Let's say that has grown to about $30K (it would probably be higher, but I'm being conservative). Even with your numbers of $20K/year, that really only leaves about $50K for them to pay. Let's say they can put another $5K a year in and the kid can work during the four school years for a total of $10K (again, probably on the low side).
You're left with $20K that needs to be taken in loans.
So, well within the means of the average middle-class family, with a little planning.