Frank,
The ethanol of course absorbs water and that causes gas tanks to rust and carb internals to corrode. Then the ethanol also attacks the resin in the fiberglass tanks, and as you mentioned, rubber and plastic in the fuel circuit to include petcocks, fuel lines, gaskets etcetera. Then organic stuff grows more easily in ethanol than in straight gas so gunk clogs jets and impairs float needle movement.
Then too, it plays heck with the little two stroke pumper carbs that are on all the various pieces of garden equipment and the EPA, for fear of smog, long ago dictated that all of those little carbs' be sealed so people can't adjust them; there are tiny pressed in caps that cover drillings and tiny fixed jets underneath such that it is not cost effective to even try to clean out the clogged jets. You spend a hundred dollars, more or less, on a weed wacker, or a hedge trimmer, or a blower, or a chain saw, only to have the gas kill it inside of a year. The only way to prevent it is to make certain that the carb is run dry when you put it away. Lawn mowers, with their conventional carbs are easier to fix when the gas clogs them.
I try to run my motorcycles dry too, although right now one of the carbs on my old GSXR is clogged in the idle circuit and it is a pain to remove that rack of carbs from those thirty year old stiff intake manifold/carb boots; not to mention the risk of cracking that old rubber.
Edit - And Comnoz is quicker than me - ditto what he said.
Edit - And Snorton74 too, ditto that too.
Interestingly, fuel injected engines don't seem to suffer from it as much; the metals and rubbers are designed for it of course and then the fuel pump's and the injectors' power seems to be able to push and pound through any gunk. It may also be the total lack of air or oxygen that an injected system enjoys once the fuel is past the tank and into pressurized fuel lines/injectors.