Yes, it has been discussed many times on the forum, and it doesn't have anything to do with GSX. The reason to flag all parkings as GA, is to get rid of default ground vehicles that would conflict with the vehicles or static detail in the parking provided with the GSX.
GSX, if anything, would help you overcoming the minor annoyance of having them listed as GA in the FSX "Go To Airport" menu because, if you use GSX instead to position your airplane, you'll find them arranged in a more logical way that the default FSX system could ever do, grouped by terminal and gates, with terminal having their real life names.
To do this, position to the airport using the FSX standard menu, but place the airplane on the runway, then open GSX menu, select a parking, and the "Just Warp me there" option.