i dont think it would make a big difference, you would be prety iresponsible to go to a show with an infected horse. if your in a show ring with an infected horses chances are it would be picked up anyway just by sneezing or if horses put there noses on the grass etc.
I went to one a couple of months ago and she was feeling down their legs, ect she touched every horse in every class! she just back off one that nearly kicked her!
Yes, I would actually prefer for a judge to run their hands down my horses legs, feel their coat, muscle tone etc. (Even it it cost me a place because my horses legs were blemished, say). I think it's much more thorough. The eye can be good at judging - but it's always a good thing to add some "feel" into the equation too.