High Wing Drifter
In the ATPL they would be talking about issues relevant at airliner speeds, and yes the temp drop around parts of the wings/airframe could be a few degrees C. But not at GA speeds.
Sharpshot
Did you calibrate your OAT gauge? Also it is VERY common to see an OAT of say +4C when VMC on top, dropping to below 0C the instant one descends into the cloud.
As I've said, icing below the MSA stops me flying. But I also think that some people are excessively worried about the shortest exposure to a cloud below 0C.