All these companies make nice frames, but aside from "quality" (ie, welds, etc) what is there magical about these products?

If any of these companies (and I mean overseas companies too like Pinarello, etc) don't test various parts of the finished frame for stiffness, etc then why buy them?

OK, to answer my own question "experience" in judging things comes into play, but I often wonder what sort of engineering these companies invest in?