I was about to tell you that its time for you to go and do a litle more "research" before you continue to post more BS like this, but that would be wrong because you are well informed, the problem is that you intentionally play it dump, why?
What part of user testing by not introducing my own knowledge do you, Dan, Ned and the rest of the boyz not understand about how to build great user interfaces.
This has nothing to do with "great user intefaces" it has to do only with your suspicius behaviour.
You've obviously never worked in a commercial software development company for average user facing applications and websites. I have. I have created million user products for the average folks. You apparently don't know that every major social network runs tests with average users so they can find the rough spots in their user interfaces.
I like how authoritative(and wrong) your assumptions are but for another time you are trying to dodge here.
While automation can provide documentation and a safety net for future changes, the UI must still be judged by human senses. Experienced exploratory testers are a must, and they should consider pairing with actual customers or customer proxies to make sure the user experience is good enough.
How we test
Every day, we run hundreds of tests on Facebook, most of which are rolled out to a random sample of people to test their impact. For example, you may have seen a small test for saving news feed stories last week.
Other products might require network effects to be properly tested, so in those cases we launch to everyone in a specific market, like a whole country.
Getting it wrong
I'd like to give you an example that is rather uncharacteristic for Facebook, a product where we didn't follow our normal testing procedures or even our normal development practices. It was a feature I worked on a little over a year ago called the chat bar.