Beautiful, I'm happy for MS to make IE9 comply with all this new stantards.
Now, I leave you. I have to spend the rest of the evening trying to make a site to work and render correctly in IE6, IE7 & IE8 (at the same time). :(
Wouldn't the users that use an outdated version of Internet Explorer also use an outdated version of an alternative browser, if they had used this browser in the beginning.
Another factor about IE6 is that it's only used in organizations and companies where people can't install their own programs, so they don't bother calling up IT (sometimes outsourced IT which is expensive) just to install a browser.
Not many people run IRIX these days.
As for IE, it's not trivial to have more than one version of it installed under a single Windows image. That and internal applications that rely on a specific quirky version of IE won't help with keeping your browser up-to-date.