My take is that that is marketing hype, unless anyone can prove otherwise ???
I am now on my third set of Conti C rated tyres and only have 37,500 miles on the clock so they do a LOT of standing around and I have never experienced any kind of sidewall cracking or flat spotting. I have changed both previous sets at ten years from date of manufacture as Conti advise and there were no signs of any adverse conditions when removed, call me oversafe but that is my preference.
Keith.