John. as I stated from my post many many years ago, Dicors position on roof cleaning only changed after repeated customer requests on how to do this... Probably because of the harmless black streaks that some get. ( Here in AZ, it doesn't seem to be an issue).
Dicor obviously saw a business opportunity, and created a line of roof cleaning products. Which they now naturally strongly recommend.
As for different thicknesses. That may now be the case. But it doesn't change much.
Likely the RV manufacturers asked for lighter material so they could reduce the weight of their units.
Carlise says that the white material CAN be washed. Only to retain the reflectitiy of the material. But there is NO warranty requirement for it. AND the black material has NO washing recommendations.
For those that want to wash your roof.. My recommendation stays the same. If it makes you feel good, do it. So long as it is done right,
it won't hurt a thing....
But since I became the Safety Coordinator at my job about 5 years ago.... I must caution people on the dangers of doing so. A wet roof can be VERY slippery! The only safe way to do it would be with a catwalk scaffold system. Some dealers may have such a system. I know the manufacturer does, as I have seen it.
A fall to the ground can SERIOUSLY cripple or kill.
Be careful up there.