I recently met two people who got Ph.Ds from Australian universities who told me their stories. I found them disappointing.
Dr. A had a very senior role in government. After his contract ended he spend one year writing a thesis, largely based on his experience, submitted it and was awarded a Ph.D. He is now a Professor at a (mediocre) private university directing a research centre on government policy.
Dr. B was a software engineer. He worked part time and enrolled in a Ph.D in computer science. He would come on campus about once a month to meet his supervisor. As far as I am aware this was the only interaction he ever had with anyone from the university. He never went to any seminars, talked to other students, or took courses.
I don't doubt that on some level the theses submitted by these students may be comparable to those of other students and "worthy" of a Ph.D.
However, a colleague recently pointed out that at almost all universities the first page of the thesis says something like:
"A thesis submitted in partial fulfilment of the requirements for a Ph.D"
I think some of most important things you can learn in a Ph.D are not directly related to the thesis, as I discussed when arguing that the class cohort is so important.
A related issue is that I consider that undergraduates who skip classes yet pass exams are not really getting an education.