But, there are LOTS of fatal accidents where pilot error was cited  

"The R-44 rotor system is not unstable unless you operate it in a manner outside its envelope"

A really good friend of mine who was a competent high time R44 pilot told me the same thing after I warned him on several occasions about the shortcomings of the Robinson products. He died this year when the rotor diverged and chopped the tailboom. 

And, this is how it goes. You're a true believer in the above statement up until the moment you die.

Understand, the envelope on most machines is a constant. With the Robinson, it's a variable. 

Here is a perfect example of flying well inside the envelope and the variable rearing it's ugly head. 

https://asn.flightsafety.org/wikibase/35935