Gentlemen, and particularly Rotorfossil, you need to read Nick Lappos' comments on this in the Rotorheads section. Just do a search on "pressure bubble" or "helicopter urban myths" and sift through Nick's answers. He shoots down most of the comments in this thread, and gives the real reasons. In good instructional manner, I will not spoon-feed you, it is your job to look it up.
For those not familiar with him, Nick was Sikorsky's chief test pilot for many years.