The important thing is whether the university requires continual enrollment. This means you have to pay tuition every semester you are enrolled. At Michigan, it used to be you passed quals paying tuition, and then you did not have to pay tuition until you defended…students often held jobs while finishing their thesis…it literally happened all the time. Michigan has since changed this. I think this is unfortunate…this is reflected in the entry about why not to go to grad school.
http://100rsns.blogspot.com/2011/05/59-you-pay-for-nothing.html