Call it national pride, but given my experience with car washers from various countries I can say that Mexicans are the best at it. Maybe it isn't something to be too proud of. One thing I can say for sure, the Dominicans in my neighborhood are not all that good at it.
It is also funny how much extra attention your car gets once you speak in Spanish and then even more when you give them a nice tip. I had the guy chase me down and give the car an extra wipe as I was leaving once he saw what was in the bundle I handed to him. Even then, I had to spend sometime making up for their shortcomings.
If this anthropologist/professor gig doesn't work out for me, I always have a backup plan.