Wouldn't dream of shooting you down Super Uwe, too useful a member to just waste on target practice, but I don't think there is any rain sensor fitted. In fact, the variability, (which may be speed related, I can't say as I have noticed it myself) should work even if it wasn't raining in that case.
No worries, pleased not to be shot this time
Just remembered the rear wiper comes on when reversing when it's raining as well. Not sure if that's related to the front wipers being on at the same time or not, but it's a nice touch.