I think it is because you are able to get more travel and therefore more load in the rod. When you cast vertically you are limited to more of the 10 and 2 casting style versus when you move to your cast to the side you are able to extend your arm back. I think both Lefty and George agree as does Jarowski, Sedotti etc... that the more distance you obtain in the casting stroke the more load you can achieve and therefore greater distance in the cast. All other things being equal.
Just out of curiousity, are you shooting 95' feet or is your total cast 95' (i.e. 40 feet of line out and shooting an additional 55') either is still impressive.