Air is a medium, just like water. your example would be valid if the log rolling is under the water, and you take the log buoyancy out of the question. In other words, take a log like IPE (wood denser than water) and put it in a vacuum, and roll it. Reason the log drifts is because of the surface tension delta between the air and water. If this surface tension delta didn't exist, no drift.

Awesome questions, makes me get out my hydrolics and fluids engineering text books from college.