Besides, oils attract water molecules as it sits.
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You do not seriously believe this I hope????
If I may ask, what school did you attend that they taught you that?
If you start and run an internal combustion engine long enough to hit operating temperature then you should not have ANY water in your oil as it will have evaporated (boiling point, evaporation rates, etc etc...) If you do, you have some seriously screwd up $hat going on in your engine.
Now on to the original question as per the thread start.
Regular oil changes based on a given mileage OR time frame is advised, because, oil is also the soap and water of the internal combustion engine.
Would you take a bath in your bath water thats been sitting all month?? (I know, its an extreme analogy, but this is intentional).
The oil in your engine has detergents in it that help keep the dirt and contaminates inside the combustion engine suspended in the oil which is passed through a filter, which in turn cleans out that crap, BUT there will always be some stuff that is still suspended in the oil that the filters cant take out, ACIDS.
The service manual states to change oil roughly ever 5000 miles (8000 km) because they figure the oil, if you use their recommended oil, will be good for that MILEAGE based on REGULAR use (implies daily/weekly/and at bare minimum monthly use). Their figures do not account for people who may not use it in those parameters, and thus do not make a recommendation about changing based on a given time frame of bi-annually or greater. If you let dirty oil, with ACIDS in it (which are created every time you start and run an internal combustion engine as it is a by product of internal combustion fuels), sit for to long it can cause damage to bearings and wear surfaces that will lead to premature failure.
Premature is the key word. It does not mean that your going to see or notice the damage in one year or 2 or 3 for that matter, it just means your cheating yourself out of some of the over all life expectancy of the engine. If your someone who buys something, keeps it 4 or 5 years and then dumps it on the next fool with money, then why bother ever spending a dime on an oil change? It's not like your stealing anything away from YOUR overall enjoyment of the bike and you will save roughly $60 per yer. Heck you can go out someplace nice to eat, once by yourself, for that kind of money.
But if your a true believer in taking care of the planet and keeping and maintaining your stuff for peek efficiency and performance, and you want your stuff to last you as long as possible on a minimum outlay of $$$ through the years, then you would be well advised and money ahead to change it as per an oil test would advise you, or at least based on the service manual recommendation for oil changes with at least once a year (at the end of the season before storage for long term) being a minimum.