Why would you want full beam on with fog lights, in my 30+ years driving experience the backscatter/ glare in any form of fog even on old style halogen headlights on full/high beam is so severe that you have to switch back to low/ dip beams anyway. The only reason I can think for wanting them on is to use them like driving lights, but they don't have the reach or spread for that. The rear fog lights stay on because the idea is to allow following drivers to see your car at a greater distance and hopefully prevent them from tailgating you.
In the USA you need to check the DoT 49 CFR 571 regarding the positioning and use of foglights and that will answer why your great leaders over there don't want you to drive on front fogs along with high beams. You may also find this website "illuminating" if not educational!
http://www.garageboy.com/fahrt/fog.html
The US DoT CFR is here
http://www.nhtsa.gov/cars/rules/rulings/glare.html