In your kitchen cabinets, do you place your cups and glasses upside down? If so, why?

In a recent trip to visit my son in Seattle, I noticed that all of his cups and glasses were upside down inside in his kitchen cabinets. I stood there and wondered why he would place them there in this fashion. He has a dishwasher and the cups and glasses are dry, when finished. I have never placed these items upside down in my kitchen cabinets. Question: what reason could my son have for placing his cups and glasses, this way, in his kitchen cabinets? And, no I did not ask him why.