According to the rules, wagons can pass through hedgerows unlike trucks.
Given the nature of the Normandy bocage, surely a horse drawn wagon would struggle to get through the dense vegetation even if it could get over the raised bank? And it would be even more difficult towing an artillery piece.
Fair enough if Engineers had created a suitable breach beforehand, but then wouldn't the breach be accessible by trucks too?
I think we need to look at "wagons" as a generic term for horse transport. Most artillery limbers would have been hitched to a harness and not a wagon and the harness would have been hitched directly to the weapon with no "vehicle" between the wrong end of the horse and the wrong end of the gun. Under those circumstances we are comparing the ability of a horse to get through the hedgerow with a trailing weapon and the ability of a truck to get through with the same weapon. If we assume that the weapon can make it the horse certainly can but there is no guarantee that the truck can. Of more concern would actually be the ability of the ammunition supply to get through the hedgerow.
As to whether the movement point penalty for such an action is sufficient I can't say.
Yes, these has been one of those holes in the system. Given that the wagons are "foot" units for movement costs, this allows it to technically go over the hedge with just a +1 MP. Same thing could be thought of with bicycle units as well.
Keep in mind that the hedgerows weren't grown to keep farmers from bringing horses, plows, and wagons for the harvest out of the fields. They were planted to prevent erosion of the soil. There are at least one or two "fords" in every hedgerow. Of course using these gateways subjects you to sniper fire.