Catchy headline, but there's not much to the conclusion
The Washington Post article isn't a new study. The College Board released the data last October. Moreover, the data itslef is five year's old. It measures a period, 2008, before the Great Recession and legislatures began major budget cuts.
Second, it only looks at the difference between the published price and grants. To the extent the student borrows money, it is not reflected in the results. As the note at the end of the College Board's table indicates, it also doesn't reflect the impact of available tax deductions and credits. See, http://trends.collegeboard.org/college-pricing/figures-tables/net-prices-by-income-over-time-public-sector.
I will be posting on student debt in the coming days.