Big corporate is such a weird space.
On one hand, you're right: big corporate will block this, and that will limit the impact, and thus I think a lot of the hallelujah in this thread is over-optimistic. But MS would never force such consequential upgrades on those customers; that's part of why MS owned and still owns the "enterprise" market (decreasingly lucrative though it may be).
On the other hand, I doubt that consumer adoption driving sites to drop support for IE6 will have any substantial impact on what megacorps decide to deploy.
One of the things that really blew my mind this year was a large ($40MM) software development project I became familiar with (a worldwide internal system for a multinational corporation) that concluded -- in 2011 -- and required MSIE 6. MSIE 6! Doesn't even run on MSIE 7, much less any modern browser.
While I personally think that's insane -- if you are that specific (not to mention antiquated) with your browser requirements, why don't you just code a native app? -- I've also never developed software with a team larger than five, and certainly don't know the nitty-gritty details about spreading the work over a dozen countries and hundreds of developers, the vast majority being low-cost Chinese and Indian coders. So I'm not judging (or at least I'm trying not to).
But my point is that Big Corporate just wants their freaky "web-based" apps to run predictably for the projected 6-year deployment timeframe and does not give one flying fuck about whether their staff can access the new hip and way-superior version of . Unless said had real business value to large enterprise, but then, if it did... it would probably support MSIE6.
So while this news is welcome, it's still unlikely that the computing capabilities of the typical large-company locked-down employee PC are going to become awesome, or even good. Even MSIE8, while way better than 6, still isn't something you jump for joy having to develop for.
This matters less and less, though, as the percentage of people who have a way more capable browser in in their pocket increases. So I think that it is starting to make a lot more sense to give up on corporate machines and dead-end legacy browsers, and instead spend that effort on scaling your app's interface to smaller form factors.
(Disclaimer: that's what I think, but not what I actually do. I work on web-based software for medium-sized businesses, so I don't have to worry much about what browser users happen to have. In this context, you can have requirements, and I tend to just say, 'In order to decrease development costs, the system requires the Google Chrome browser. But don't worry: it's free, secure, cross-platform, and has become the dominant web technology standard.' That last part is a bit of customer-reassurance hyperbole, but so far, no problems. (And of course the same code typically works fine on Safari if there's an iOS requirement.))