|Quoting Klaus (Reply 34):|
And if the wikepedia explanation is correct, autorotation-enabled rotors already have a spanwise-variable pitch built in which even becomes negative along the inner span in the lowest collective range.
And that is why you do not quote Wikipedia. The aerodynamic twist of a rotor blade is the opposite of what you quoted, the blade TIPS are always at a lower pitch angle than the inner span.
This makes sense for a couple reasons. First, the tip of the blade has air flowing over it much more quickly than the inner part. This means the blade tip needs a lower pitch to create the same amount of lift as the inner portion. This also helps keep the blade tip from stalling at high pitch settings and high forward airspeeds.
During an autorotation, having the the blade tips at negative pitch ( only a few degrees at best ) provides rotational force to the rotor system in the desired direction, and it does this in the most efficient way possible by applying the force at the end of a long moment arm.