It's just gravity, right?
I'm not sure if it is still done but most manufacturers used to take the term "dry weight" in a very literal sense. They always excluded the battery! That's right, that 10-20 pound box of lead most of us have. Since it had "wet" stuff in it they would pull the battery, together with oil, gas and radiator fluid to arrive at a "dry" weight. (oh yes throw out the tool kit as well) They probably even excluded brake fluid. The "ready to ride" weight is what matters. As to gas I say 2.5 gallons for everyone. Good enough for 100 miles or so for most bikes, costs about $10, and I can remember 15 pounds. Now if you want a real debate maybe some of the aero folks can run the numbers on center of gravity, effort, etc. for our trusty steeds. I'm sure we've all ridden a light bike that felt heavy and a heavy bike that rode light. Measuring the gravitational attraction to the center of the earth (i.e. weight) is just one measure. Thanks, Rich
p.s. My KLR weighs nothing while riding upright, about 400 lbs in the truck and weighed 2 tons when it fell off the loading ramp.