Two components of indentured servitude is that they do not permit you to leave your work until you have paid the debt, and secondly that they charge you so that you can never escape your debt. A final onerous part of real indentured servitude is that debt can be passed to your children, and many generations can be born into slavery and never leave it. [Source: Disposable People]
[edited to remove bankruptcy reference. Apparently it doesnt help]
Of course, it's not going to follow for generations, so you're right about the situation being substantially better than indentured servitude. But the metaphor isn't too far off the mark if its context is toned down a bit.
Prisons making you borrow money would be indentured servitude. College loans is taking a loan.
There could be a case made for credit cards being indentured servitude, due to their unreasonably high interest rate and the fact that they entrap you by just issuing them. Far more so than college loans.
You could probably find millions of people, including me, who would gladly trade their student loans for several years of indentured servitude.
My history is a little shaky on old American slavery, but I'm pretty sure that a large number of indentured servants brought to colonies in the Caribbean were disposable: they were worked til they died and never managed to leave their servitude.
What I am saying is that college debt from middle class 1st world adults is not indentured servitude.