When I changed my oil the other day I found the oil to be only slightly warm even after a 15 mile ride. The temperature gauge was about the 1/4 mark after riding for about 5 minutes so it appeared to be warmed up. Seems to be pretty common on most motorcycles when the temperatures get below 40F. Especially those bikes fitted with an oil cooler. I suspect its just the way it is and as long as the oil is changed regularly its nothing to be really concerned with. Fresh oil is loaded with anti-corrosion additives.
Now during the summer the oil can get rather hot even during short rides. Pretty strange how ambient temperature can have such an affect on the oil temperature even on longer rides.
Yeah, it's part of what gets taught in many physical science courses. (Flashback time!)
The greater the difference between a heat source and the substance that absorbs that heat then the faster the heat is transfered. If you're driving through 100 degree air and the engine coolant reaching the radiator is 185... then the difference is just 85 degrees. When you drive through 40 degree air then the difference is 145 degrees... so the air can absorb a lot more heat per cubic foot. Temperature equilibrium is when the engine reaches a temperature where the heat made is the same as the heat lost.
Our little 500 twins, like all common internal-combustion engines, lose most the combustion heat out the exhaust. The rest conducts through the engine/oil/coolant to heat those things and can reach cooler air.
So in cold air it makes sense to diflect cold air from running right through the radiator, as FOG shared.