Maxter, I hope you're still reading this.
The professional GPS equipment you're using. I've always assumed that such equipment, used for mapping purposes, is mounted on a tripod or something and has a button or something that allows you, as the operator, to tell it that its position is now fixed. From that point on, the receiver can start collecting GPS positions and average these positions out over a longer period of time (minutes, hours, perhaps weeks)? This, combined with a differential GPS broadcast device, set up locally, in a known position, will then give you 2cm accuracy, not?
But an average consumer GPS (up to and including the G-1000) will not have the benefit of a "steady state" button, so it has to assume that it's moving all the time, making averaging over a periode more than a few seconds impossible, and will not have the benefit of a locally produced DGPS signal so has to rely on WAAS, if WAAS is available for that area at all. Hence the 6-35 meter accuracy for these devices?