"Working" means that it works now. "Supported" means if it doesn't work in the future, you can file a bug report.

Not saying they shouldn't sniff for ie 9+, but it costs money to support browsers, especially when you are not developing on windows.

I might be bitter about this, but I have literally spent the last two week working on frustrating to debug, and hard to fix css and javascript issues in ie 7 and 8. Our customers want IE support (companies that don't want to "vet" things they don't have to), and we want to give it to them, but it is getting to the point that it costs us too much money