The cheap accomodation is usually flooded well in advance by foreign students (summer schools, etc - the name sells very well) and the university is quite good at squeezing money out of visitors.
Mind you, we managed MIT, so...
Not that the person with the Dunelm email address is at all biased. ;)
I imagine Oxford is one of the most expensive unis for holding conferences in, simply because it's Oxford.
MIT has a strong interest in things like Wikipedia, so that probably helped there. Oxford has no such interest...