User testing is great, and very useful for so many people.
BUT, when you're the size of Google, or Facebook, or Microsoft, Things look a bit different.
Most people are far more conservative than they realise, but also, perversely, adapt quite quickly to change if they experience it day-to-day. This means that if an interface has enough inertia, then a change that performs badly in user testing, can actually quite quickly be accepted by people. (PROVIDED it's actually better).
In the first example, every change to the Facebook UI is met by a barrage of criticism and hatred, but they seem to actually make good decisions, so the changes get absorbed by users, and things continue.
Having said that, Microsoft struggle, because they often make changes that are fundamentally bad decisions, and have to back-down. For example, the Office ribbon took a while to be accepted, but is /generally/ liked nowadays by people, because it was functionally a good change (yes, some people will disagree, but the majority wins on this front). Taking broad user testing results on the ribbon would probably have stopped microsoft from progressing with it. On the other hand, the 'Metro'/Tile UI in windows 8 was an actual usability disaster, and has forced them to revert to a more common pattern until someone can design new metaphors that actually improve usability in windows.
Finding test subjects that aren't used to, and comfortable with, the google font/design styles, to give objective feedback on a change, is really hard.
[ I didn't mention first time round, but I /really/ don't like the new logo, that lowercase g makes me cringe inside every time I see it. ]