If I, as a developer, decide my site supports a browser, I know I'm going to have to spend some time doing QA on that browser. Standards are cool, but I've run into enough FF and Chrome bugs that I always test.
That being said, the cost of testing in IE is waaay higher than the cost of testing in FF and Chrome. Why? Because FF and Chrome are cross-platform, I and my fellow developers can test on our OS of choice. With IE, a testing environment costs my company about $300 per developer.
Not to mention that setting up a VM for testing is the opposite of straightforward. After shaving a few yaks to convert the stupid VHD format to something VirtualBox can understand, you need to hack your local network so the VM can see its host.
Also, the developer tools are crappy. Has anyone worked on those in the last 10 years? I use Chrome for development not because of "web standards", but because the debugging tools are awesome (some people swear by Firebug, also, YMMV).
So I guess the point "support" is a little more complicated than "look, it works!".