I equate the "energy left to flare" concept fairly closely between fixed and rotor wing aircraft. Though I have not attempted it, I would imagine that a stabilized autorotation could be achieved at less than the minimum specified low rotor RPM. When you got to the ground, there would be little or no reserve energy in the rotor to be available to create upward acelleration of the helicopter to reduce descent rate. Landing gear testing....
I do have considerable experience with the differences between normal, and STOL kid equipped aircraft. The STOL kitted aircraft may demonstrate a reduced power off stall speed. This could lull the pilot into a false confidence that a reduced glide speed is safe. The lower glide speed is possible, but the pilot has now surrendered the extra energy reserved in the aircraft, which will be used up to change the direction of the aircraft from somewhat downward, to hardly downward, along the runway. Thus, when the pilot pulls to flare, the aircraft cannot accelerate upward (which would simply be a reduction in downward speed), and just impacts the runway at the extablished descent rate.
As for the Buffalo accident, I have more than my fair share of knowledge about that one. I rode over to Farnborough on that aircraft, and was a jump seat observer for the show demo flight, two days before the accident. I had a limited background role in the investigation. The reduced energy to flare was an aspect in that accident, but it is my opinion that other factors were large contributing factors too.