Yeah, it is extremely confusing. I was of the opinion that the weight of the loaded trailer couldn't exceed the weight of the towing vehicle.

eg, A Holden van towing a car trailer could only tow a car that weighed a lot less than the van. I have seen vans towing other vans, which doesn't seem right, and down my way every tourist has a boat and there's some BIG ones that are being towed by all sorts of cars that seem inadequate. I don't know how they make it back up the boat ramp (or the trip here from Canberra).