This is all interesting to me and leads me to one obvious question. If there were no legitimate reason for directional tires to be mounted, well, directionally, why the heck would they be manufactured and sold as "directional?"
I am no tire expert. My last car used 14" tires. During the last few years I owned it the selection at tire retailers was consistently shrinking. I bought a set of Goodrich T/A touring tires at Sam's. I got a flat from some road debris. It looked, from the outside of the tire, like it was punctured in two places. They told me they could not fix it and no longer carried the tire I had. I did have road hazard coverage so they offered me a "deal." (NOT) Even after conversing with the manager, my "deal" was that they could replace it with the tire they had in that size now, but since it was "directional" they were only allowed to do it in pairs. Were they going to make me right at no charge? No! My offer was that I could buy the two new tires at a price based upon the percentage of tread on my current tires - $130 for two new tires. I did not take them up on the offer. They would not even let me leave the store without installing my spare for me. Ugh! when I got home I pulled the piece of metal from the tire and it was only punctured in one spot. I plugged the hole myself and went on my way. Do you think I am likely to buy tires at Sam's again? Right. Nor do I plan to ever buy directional tires if I can help it. I generally only rotate front to back, but having the option to swap sides is nice.