Why do higher education cost increases outpace CPI?

Interesting blog post by an economist and even more interesting responses.

http://www.marginalrevolution.com/marginalrevolution/2007/10/why-do-college-.html

Some of the arguments are:

1) Other people are paying, so real costs are hidden (government loans, parents, merit scholarships, etc.).
2) Baby boom increases competition (which means we're all in trouble in the coming baby bust).
3) Baumol's cost disease (fancy way of saying that service sectors don't see productivity gains, so their inflation rates are always higher than CPI - http://en.wikipedia.org/wiki/Baumol).
4) The cartelization of accreditation agencies.
5) People are getting richer.
6) ROI on education has increased dramatically.

And here's a version focused more of public institutions and why this author finds most of the arguments uncompelling.

http://www.insidehighered.com/views/2007/11/02/callan