I do some limited IT support for a large (140,000 employees), multi-national defense company. Everything is IE6, and IE6-only. If I use IE9 to access our internal apps, it complains I have an unsupported browser.
I know our competition works the same way, as does pretty much the whole government services sector. That's a few million employees in the U.S. alone.
It's great to have a washing machine that works for 10-20 years, but why couldn't the government and corporations pick a _good_ washing machine. Why IE6 instead of some sane browser?
Anyway, there's enough non-IE6 work to do that I generally refuse to write any IE6 code (and when I do, I don't spend more than a minute or two copy-pasting some conditional comment found via Google.)
Why a Motorola Razr instead of an iPhone 4S? Because the latter didn't exist. When IE6 came out more than a decade ago, it was the absolute best browser available. In 2004 when XP SP2 came out, it cleaned up a lot of reliability and security issues. You just have to look at IE6 with a 2001-based lens and realize what the alternatives were at the time.
IE6 was good enough to become the standard for slow-moving corporate types, and they're sticking with it. The every-few-weeks upgrades of Chrome and (now) Firefox are way too fast for them.
A lot of these big companies will stay with IE6 till the bitter end in 2014, when free XP support (security patches) goes away. I wouldn't put it past some of them to pay for XP support rather than switch to another OS, or to negotiate extended XP support into their Microsoft upgrade contracts.
I know our competition works the same way, as does pretty much the whole government services sector. That's a few million employees in the U.S. alone.