[etendue]

The attrition rate for a PhD program isn't 90%, but 50% is not unknown; my own was around 30% (measured from matriculation to defense, my class year). Some students were forced out of the program, others left on their own accord.

Also, it is unusual for a dissertation to be outright rejected because of how it reflects on the advisor and committee: the committee is (supposed to be) kept up to date on the student's progress and will recommend against defending if the student is unlikely to pass. Slightly less unusual would be a student being allowed to defend, but then needing to do major revisions to their dissertation for it to be accepted. Keep in mind that at the point one is defending, quite a bit of time and money has been invested in the candidate so there is a good incentive to see the candidate succeed for no other reason. Unsuited students are (ideally) dismissed much earlier, i.e., at admission to candidacy.

One absolutely worries about being scooped on papers, since those are the currency of academia and being scooped usually results in needing to publish your own (now less novel) work in a lesser journal. And as another commenter points out: a professor taking on 10 students with only 1 succeeding, if one defines success as being tenured, isn't that far off from reality.

As an aside, I personally think forming a research group at a university isn't all that different from creating a startup.

[tjl]

I've known students who defended their thesis and were told to do major revisions. Typically, it's because their thesis supervisor didn't do their job properly as they should know not to send that student to defend.

You're right in that they weed Ph.D. students out earlier, during their comprehensive exam. How it's done varies from department to department and university to university. My comprehensive was a lengthy oral exam by my committee with two rounds of questions. The first on background and the second on the written thesis proposal I submitted. I went for 3.5 hours straight, basically until the committee wanted lunch.

Equating a research group to a startup isn't a bad analogy. One of the professors in my department basically uses his students to do research for his company. He even makes them sign over the IP rights to him. Other professors have a continuing line of research across a number of students. Even my Ph.D. thesis was the latest in a number of theses on the same topic, each getting progressively more advanced. My thesis basically finished that line, with other related ones opening up as a result.

[Chyzwar]

Nope, research groups/projects at uni is all about milking money from grants. Running startup is all about making money for investors. Direction is different and risk much lower.