It is the manufacturer who sets Vne!!
In order to get certification of a fixed wing design the manufacturer has to NOMINATE a speed for the design known as V design (Vd). If he succeeds in demonstrating in flight that all is well under these conditions then he is REQUIRED to reduce this by 10% and set this lower speed as Vne
Dangerous aeroplanes are those where there is enough power to exceed Vd in level flight or with a small rate of descent that could arise from a moments inattention. There have been one or two examples of this problem in the past and (reasonably) they have attracted a Vne lower than 90% of Vd.
Some aircraft in development programmes get modified for various reasons and this can call for an even lower Vne to be set temporarily. I believe this was one factor in the Vulcan accident referred to earlier.
Please note I am not saying identical rules apply to rotary wing certification as I have never been involved with that. But I would be surprised if the situation with choppers was not similar. Perhaps a rotary wing tp will comment.