Global numbers are always going to go up, but US numbers are where the prestige is and what Wall Street pays attention to. US numbers are the canary in the coal mine, or so the thinking goes. Same for Netflix's woes, they're trying to offset US declines with global expansion, which looks nice on paper (or in hasty PR statements explaining why things are Just Fine, Promise) but US users will always be far, far more valuable to stockholders and also advertisers (even advertisers outside the US).
The Facebook Monster has finally stopped growing, it's the turn of the tide. Now we just need MySpace Tom to return like Gandalf the White.