It proves that the technologies are capable products at the most massive scales. Do you have evidence to support that Facebook, Tumblr, or Etsy would have been better off had they chosen different technologies (of course not)? Or that they made things more difficult for themselves? How would Facebook be improved by PostgreSQL? At scale, data is so massively partitioned that the fact that you don't have windowing functions is utterly irrelevant. I hate PHP as much as the next guy, but the facts are that it gets the job done. And that, in business, is what matters. The angst on here about MySQL is unfounded and is largely a symptom of groupthink.