BEagle,
You are absolutely correct, you cannot underestimate fatigue. I have not found it to be a problem among pilots. Pilots know their limits and stop when they reach it. The only people I know that continually under estimate fatigue are the airline dispatchers. They will always try to push you into one more flight, but that is a story for another forum at another time.
I noticed you are an Instructor and an Examiner. I was wondering in your experience, have you seen the quality of the students you examine diminish as the instructor's training load increases? If so, at what point does it go down?
I am guessing (educated guess) that the 100 hour limit is just like saying "everyone will from now on wear a medium size shirt". For some, the 100 hour limit is too high, for others, it is too low, and for a few, its just right.
Chuck Ellsworth's signature really hits the nail on the head.
The hardest thing about flying is knowing when to say no.
Take Care,
Richard