Furthermore, not finishing a Ph.D. is not exactly uncommon. Click on this slide show about Ph.D. attrition rates from the Council of Graduate Schools, and note the following three facts:
1) Only 46% of all entrants finish their Ph.D. after seven years in a program.From that report (written in 2008, collected from data before then) the 10-year completion rate was 62% for a doctoral degree in chemistry. (I wonder what that number is now? To SESTAT!)
2) For social science Ph.D.s, that figure is even lower -- 41%
3) If you extend it out to ten years, the lowest completion rate among the social sciences is political science -- only 44% complete a doctorate after a decade. In other words, entering a Ph.D. program and then not finishing is the modal outcome.