That's not really true at all. I tour on a 35lb Raleigh and fully loaded feel very stable, even doing 50kmh downhill. I also have a stripped down clubman style Norco weighing probably -20lb that feels twitchy as hell. It has more to do with fit, bike geometry, frame stiffness and weigh distribution. As far as an RV vs Porsche.. probably in many ways the RV is more stable. When touring I'm looking for predictable trajectory more than micro responsiveness. A well balanced loaded rig should be easy to ride mindlessly for many hours a day. I don't want a bike that will veer into traffic when I sneeze.