[Update] For Google Apps, Google no longer supports IE7. YouTube support for IE6 was dropped a year ago, and they make a lot of ad money from YouTube now.
After all, Google still happily sells clicks to IE 6 users. If you're business relies on external ads and optimizing conversion rates, IE 6 remains a priority.
For search results it's probably more worthwhile and not as hard to support the IE's but for their other apps they say they are only supporting that two most recent browsers.
I would actually argue that Google Search is still supporting IE6, just as a degraded experience. Dropping support all-together means they just ignore it exists, which is far from the truth and likely won't happen for 5+ years.
And, yes, I can give a few examples were the webdevs ignored legacy browser support and got burned.
But just last week, another subcontractor apparently didn't realize that our government client was stuck on Flash v9 and spent the next two weeks trying to sort it out.
And it hasn't happened in a few months, but we used to get occasional complaints from clients stuck on Safari v4.
Sure, a small chunk of the pie, but still a large chunk of people. And, in a hypothetical situation where your % of revenue generating visitors is exactly the same as for the overall population, not many companies would want to lose 2% of their revenue, or profit.
That said, I would think that Facebook is mainstream enough to get it's fair share of non-technical users.
I optimistically hypothesize that users are less likely to access Facebook (or most other non-internal webapps) from a locked-down corporate desktop, and even if not, that those users also access Facebook from non-corporate systems, making the loss of access from the corporate system partly illusory -- if the posited loss is "2%", I think the actual loss is probably as low as 1%.
In some cases, it may cost quite a large amount to continue to maintain and patch sites to also support IE6, and that money needs to be deducted from the 'profit' had from IE6 users. And more to the point, that same money being spent supporting those IE6 users could be being spent on bolstering mobile device work, newer browsers, assistive technologies, and what not.
The "well, we don't want to lose the profit from our users" has been thrown at me in the past, with the charge that "well, techies just care about gadgets/technology". No... in reality, many of us in the trenches (not all, but many) end up being better positioned to see the real business effects of these decisions. I'd much rather be working for a company that was spending its money wisely and being forward thinking rather than reactionary and wasteful. That's not a tech issue - it's a business issue.
Then there's opportunity cost. Time and budget spent on supporting IE6 could have gone into additional features. It's true that supporting IE6 is a business decision and it could be worth it for some companies, but even that 2% statistic makes IE6 seem a lot more relevant than it really is.
I'd also posit that while 2% may seem like nothing for a site with a small flow of traffic, it equates to a lot of money for a high volume consumer-oriented site. I run into a lot of this through my affiliation with Mogotest. During our customer development process I was amazed to find that several of the CTOs I sat down with will support any browser with greater than 0.5% share on their site. And these are guys that have definitely done their cost/benefit analysis.
Making things look great in IE6 often involves many hours and sacrifices of chickens to dark gods with names that have lost all their vowels.
If you're a social media startup, the customers looking for social media solutions are probably also the folks who are NOT running IE6.