To many people IE6 is the WinXP/Office2003 of browsers. It may be technically inferior to its successor, but it works the way they're used to, and it runs on their current platform. Microsoft has shoved a bunch of unwanted UI overhauls down the throats of its users with IE7, Vista, and Office2007, and I know a fair number of people who are sticking with the ones before those because of that. And if they can't (as Google seems to be telling IE6 users), then that's a good time to explore other browsers, other OSes, and other office suites.