While many of your points are valid Rich, and yes, it would be an ideal world to pump the tank dry every fall. However, I don't have an oil burner or a tractor or anyplace to get rid of the fuel. There are a couple of factors in this process of winterizing you have left off which I understood to be the driving force behind all of this winterizing/additive/topping off.

I submit the following for consideration.

a. The tank contains fuel and air.
b. It is usually a metal tank.
c. the tank is vented to the humid/wet atmosphere.
d. there are wild temperature fluctuations here in the great white north during winter layup which usually includes warmish months of October and April.

The theory of "topping up" is to replace the maximum amount of air in the fuel tank with fuel. This does two things, it minimizes the amount of air in the tank, which minimizes the amount of air that moves in and out of the tank vent when the tank contents expands and contracts. It also minimizes the amount of internal tank surface which is available for moisture from said air to condense on when the outside temperature gets cold. Therefore, in theory the fuel just gets cold and warm and very little moisture is available to get absorbed.

IMHO of course. The old timers told me to top off, gave me this explination which sounded reasonable?