Well, if white shirts were that big a problem you would have an awful lot of brides being very unsatisfied with their wedding images.
Most of the problem with white shirts is that they are metered from the camera, reflectively. If a flash meter was used, assuming there was a need for flash, the meter should give you the settings to expose the scene properly. If no flash is used a good meter will still give you the proper exposure settings.
But you are correct, using a 580EX in ETTL can be a challenge with white clothes.

