Maybe a physicist can step in on this one - in my experience, which is pretty extensive, it's just not true. Any two wheeled vehicle is more stable, whether in a straight line or a curve, the faster it goes. I think it's due to centrifugal force, but I haven't paid much attention to that sort of thing since grade school. Anybody who's ridden a Gold Wing, a BMW K1100LT or K1200LT (notoriously top-heavy bikes), or a big Harley, can tell you that they're potentially a ***** at parking lot speeds and easy to drop, but just fine once you're at speed. Not that I do it regularly, but I've ridden a couple of bikes for miles on end (in the Nevada desert, equipped with Throttlemeisters or Wrist Rests) without my hands on the bars on a long ride at freeway speeds to rest my wrists. I wouldn't dream of doing that at low speeds. Any other riders care to weigh in?