(Started out as a comment on Beren's answer, but this is rapidly getting out of hand...)
Some American universities have deals with professional printers-of-theses, which means that anyone wanting to get a copy would have to buy one through their services; the university cannot distribute them, although inter-library loan ought to be still possible. Very annoying...
On the other hand, European universities would be a lot more likely to take pains to make their work available. I know for a fact that French ones do, there is even a central on-line repository, but honestly you have to know where it is and even then it can be quite daunting to navigate.
Indeed, even though I had a fair idea where to look, it took me several attempts and dead-ends to find this link for France:
Given how tricky this can get, I'm leaving this CW so that anyone who feels like it can add in links for other countries.