Some choice quotes from a conversation recently with John at Abovetopsecret's website:
It [VMO] is an aerodynamic limit which will activate the overspeed warning horn which is very loud and very annoying and its made that way so that there is no misunderstanding about what it means. It means 'you are going too fast." To suppose that an inexperienced hijacker was flying a profile with incredible skill at 787 feet per second with the overspeed warning horm blowing is to ignore reality. It could not happen and it did not happen.
No they don't. That statement is complete false. VNE applies to propeller powered airplanes or those certifcated under the old CAR 4b. VMO is velocity max operating, MMO is mach maximimum operating. And those limitations are all that are given to the pilot, printed on the airspeed indicator and published in the limitations manual. VD and MD are certification limits and are much higher but not to be used or even known about by other than certification test pilots.
The VMO is a speed limit for descent from altitude such as towards an airport and is normally intended to avoid structurally harmful wing bending. This is not the VMO limiting factor for the 757/767. It is not the maximum speed at which the aircraft may be flown.
This statement is incorrect and absolute poppycock. It is most definately the maximum speed at which the aircraft may be flown.