^ I mean purely in terms of engine lubrication, of course. In the 400 there's separate oil supply for reductor box and engine, not like in most motorcycles where oil has to work in clutch, gear and engine departments simultaneously, so more simple car oil formula might not be a proper fit.
I understand you. And I do believe that in some cases motorcycle oil is labeled for marketing purposes. Amsoil, a few years back, sold their 10w40 HD oil as motorcycle oil, and would readily tell you if you asked. They told me that people wouldn't buy it for their bikes without the label; motorcycle shops wouldn't even stock it without the label. But it met all the specs, and they sold it at the same price, so I saw nothing wrong with that and used it for years. They have since come out with a motorcycle-specific product.
I used plain old Pennzoil for decades before switching to a full synthetic. It met the specs of the manufacturer, and gave me no problems. That was before the evil Energy Conserving spec, though.
FWIW, I do use a motorcycle specific synthetic now in all three bikes, but I really don't believe the word "Motorcycle" on the bottle is as important as the specs. I won't use an oil that doesn't meet the specifications.
The only reason I could see to do so would be to save a few bucks, and when the savings are calculated over the life of the bike it's never seemed like enough to take a chance. Maybe it'll be fine, but .... what if it's not?
Sorry if my other post seemed sarcastic. it was not intended.