Lord of the Rings - thanks for the link. It completely disagrees with the link I provided. It shows that riding 10mph in a 10mph headwind takes about 1/2 the power of riding 20mph in still air.
I think the reason for this is given by Jinker.
However, the equation (Power = force X distance / time) falls apart for a stationary bike. Just because you are not moving are you producing no power?