I don't think I know any active researchers at ProdigalU who shirk this bit of service. After all, if someone attempts to blow it off, their own students will have problems finding examiners. When the science is good, the writing is at least adequate, and the student shows up prepared at the defense, it is an awesome (if time-consuming) experience, particularly if I knew the student throughout their progress in the program. When the science is boring (or bad) and/or the student shows up unprepared, it is unbelievably awful.
It takes me a minimum of 2-3 hours to read a thesis that is well within my research specialty, longer if it is outside my areas of expertise. And longer still if I am one of the report writers. I take this responsibility seriously--after all, this is a key part of my job as a professor. It does a student no favors to grant them a PhD they can't back up with PhD level work when they go job hunting. Also, when ProdigalU hands a student a PhD, it has the same meaning whether it represents the quality work of a well-trained researcher, or the minimum acceptable work of someone pushed out after time served. Students (rightfully) get upset when they perceive that someone is granted a "pity PhD", since they want the PhD they are working so hard for to be a credential of quality when they move on to their next stage.
It makes me really annoyed at the PhD supervisor when someone shows up unprepared at a defense. It wastes my time doing the evaluation. It suggests that the supervisor doesn't care much about the quality of a PhD (or of their own trainees, for that matter). Most painfully, it makes the evaluation really difficult and take a long time. ProdigalU has public PhD defenses, so it is painful to watch a student struggle at a defense in front of colleagues, friends, and family.
As for the evaluation committee, it is always hard to know where to draw the line--should we pass a student with an acceptable thesis if the defense was a disaster (I think no)? Should we pass a student whose talk was fine, but couldn't answer questions adequately (I think no)? Should we pass a student whose talk was awful, but did a good job with the questions and the thesis (I think yes). We all have different lines, and many of us feel pretty strongly about those lines. It can get very contentious in the committee, especially if they supervisor really wants the student out and graduated.