Think about this: The manufacturer has to design the helicopter to be flown by pilots of all skill-level from Private up through ATP. Not every guy that flies their new machine is going to be Chuck Aaron. They have to assume that some dope will take the thing up with it loaded to max gross and with it also at one of the (longitudinal or lateral) c.g. limits. And maybe they'll fly it up at its limiting airspeed. Sooooo...let's see what the FAR's say about this.
§27.143 Controllability and maneuverability.
(We'll disregard letters 'a' through 'd' for now so we can focus on the really meaty part of this standard, which is 'e' and especially 'f'.)
(e) The rotorcraft, after (1) failure of one engine in the case of multiengine rotorcraft that meet Transport Category A engine isolation requirements, or (2) complete engine failure in the case of other rotorcraft, must be controllable over the range of speeds and altitudes for which certification is requested when such power failure occurs with maximum continuous power and critical weight. No corrective action time delay for any condition following power failure may be less than—
(i) For the cruise condition, one second, or normal pilot reaction time (whichever is greater); and
(ii) For any other condition, normal pilot reaction time.
(f) For helicopters for which a VNE (power-off) is established under §27.1505(c), compliance must be demonstrated with the following requirements with critical weight, critical center of gravity, and critical rotor r.p.m.:
(1) The helicopter must be safely slowed to VNE (power-off), without exceptional pilot skill, after the last operating engine is made inoperative at power-on VNE.
(2) At a speed of 1.1 VNE (power-off), the margin of cyclic control must allow satisfactory roll and pitch control with power off.
Yikes! Remember, these conditions must be met without "exceptional pilot skill."
Can you imagine being a test-pilot for a manufacturer and having to bring it up to max gross, and then load it to a "critical" c.g. (i.e. one of the limits). Then you go out and set max cruise power, and dive to power-on VNE...and then cut the engine. I'm no test pilot, but I would assume that you'd have to run that test at all of the corners of the c.g. envelope. At "critical" MRRPM. And VNE.
Scary stuff, when you think about it.
Back when we were trying to get the FH1100 back into production, an operator called and asked how fast the ship would go? I said "127 mph" (which is its VNE). And he said, "No, seriously, how fast will it really go?" I guess he was comparing it to a Bell 206, which as a VNE of 150 mph and figured it would go just as fast. And maybe it would. But an 1100 is not a 206. I told him honestly that I never took one above published VNE. Because as I said, I'm no test-pilot.
An FH1100 with a RR250-C20B would certainly go faster than 127 mph. But the mast on the 1100 is not tilted forward (as on a 206) and it has a tiny horizontal stab to help pull the tail down. Just doing 127 produces a pronounced nose-down cabin attitude of around -10 degrees. Making it go faster would make the nose drop even further. Now, can you imagine if the engine quit at "something above" VNE? Your Private Pilot natural instinct might be to quickly lower the collective. And if you did that before pulling back on the cyclic the nose would drop even further and the airspeed would increase. You'd probably cut the tailboom off or bump the mast off trying to get the nose up. I had talked with enough of the original FH1100 test pilots to know not to mess with the limits. They put the fear of God into me - and I'm an atheist!
As people have said, VNE is about more than just retreating-blade stall. A lot more.