The engine produces water, many engineers say at a rate equal to the fuel consumed (i.e. a gallon per gallon). I don't know about that, nor do I pretend to know much about chemistry, but it is clear the engine is a water factory. This moisture is created by combustion, because of the presence of oxygen and hydrogen, and normally is evaporated out of the inside of the exhaust through use. The problem is, OEM exhausts (particularly Honda's) use mechanical baffling as opposed to fabric baffling, making the units heavy and massive. It therefore takes a lot of use to heat up the exhaust enough to evaporate the moisture created by combustion each time the engine is started, and to continue to evaporate the water as the engine is used. Add in the fact that this moisture has acidic components due to the byproducts of combustion, and you have a ticking bomb as far as corrosion is concerned. (Note also that the thinner wall aftermarket exhausts, most of which also use less dense fabric baffling, rust out far slower than the stock system.) The answer? Use the bike as thoroughly as possible each time the engine is started. No short rides -- they're death on the exhaust (as well as other parts), and none of this starting the bike in the garage every so often. Forget that. If it's carb preservation you're after, the only way is to use fuel preservative. Forget also this nonsense about warming the bike up before riding. That also contributes to rusty exhausts because it warms the exhaust system too slowly. The best way to warm up the engine (and exhaust) is by riding the bike. Just postpone the wheelies and burnouts for a few miles.
Your exhaust will thank you. I have seen this principle proven among my customers who ride all different ways. The ones who fuss around waiting for the engine to warm up, or ride short trips, replace their exhausts often. The ones who don't, don't.