This part time Ph.D. thing seems a little dubious. My guess is that universities are responding to pressure to create something like an Executive MBA program so that industry people can upgrade their letters to include Ph.D…
A more traditional Ph.D. program is designed to create people capable of performing rigorous research based on deep knowledge of academic literature and an understanding of the methodological requirements for establishing credible arguments. The MA or MS or M.Phil that you get along the way tends to attest to knowledge of the literature, and the Ph.D. attests to the ability to conduct original research using sound methodological practices.
The way my advisor put it is “To get a Ph.D., you have to show that you have the knowledge to teach a good class and to write a good book (or articles).” Admittedly, “teach a good class” refers to the content of the course, not the method of delivery: the first few years of teaching are usually pretty brutal as professors figure out how to communicate the material the right way to students. It’s easy to forget what it’s like to know nothing, or to be basically smart, but not know anything. EDIT: Although teaching is a responsibility of professors, it doesn’t seem to be highly valued by universities in terms of promotion or tenure.
I can imagine a part time Ph.D. but I can’t imagine a short-length part time Ph.D. that would be taken seriously in academic circles. And the academic job market is really cuthroat right now. As Henry Kissenger said “The politics is so brutal because the stakes are so low.” Universities don’t want to grant Tenure. They’d much rather hire adjuncts for $2500 per course and no benefits.
A lot of people do Ph.D.s because they want to be called “doctor.” Perhaps companies also want to say they have Ph.D.s on their staff for marketing reasons. I guess there’s nothing wrong with that (other than dilution of the degree for everyone else), but just jump in with your eyes open.