My previous experience with thesis committees and proposal defenses have all been from the vantage point of the student. When I was in grad school our committee was established once we figured out what our project was going to be on and we had regular meetings (twice a year or so) in order for the committee to get an idea of how we were progressing. They were generally informal, with a written summary circulated prior to the meeting and then an oral update at the meeting with comments. I found it helpful to have an outside perspective on my work weigh in once in a while and I got to know my committee members fairly well. The University where I did my post-doc had a similar organization and despite having spent that time in another country, I thought that type of committee set-up was more or less standard.
I have been surprised to learn that thesis committees at Employment U. function very differently, and in my mind, defeat the purpose. Here, the Ph.D. committee is established closer to when the student is ready to graduate. I think the intention is for the committee to get together earlier and guide the student along, but the reality is that people often push the "proposal" defense back so long that it is seen as a hurdle to jump a year or so before one defends their thesis. If the committee only comes on board in the last 12-18 months, what is the point? You can find people for an exam committee anytime, but the thesis committee should be there to make suggestions along the way.
This all comes up because I have been asked to serve on the committee of a Ph.D. student and I am reading their "proposal" document now in preparation for their defense of this in two weeks. The proposal defense is also odd here and a topic for another time, but this student is looking to submit their thesis in a year or less and graduate within the next 8-12 months. Other than the proposal document (which is on a topic different from the student's direct research, by design) I have not seen anything about the student's research, nor have we sat down as a committee to discuss progress or direction and the student will likely graduate in less than a year! Again, what's the point of having a committee if not to be an outside voice? Even if the official rules allow for doing things this way, why aren't the supervisors taking it on themselves to do it differently? Yes, it requires more meetings, etc., but there are some meetings worth having and I think this qualifies. I'm sure it's just one more thing that falls through the cracks when people get busy, but we're not doing our students any favors by letting it happen.