Sure, it would be cool if every new feature of every spec were supported by every browser manufacturer instantly upon release, but it is common knowledge within the professional web development community that production sites are typically built to conform to specs that are at least several years old. It's always been that way. Sites you build, today, must conform to browsers built yesterday.
"For some clients (most specifically those in big corporates), that means having to test in ie6, ie7, ie8 and soon, ie9..."
All of the "big corporates" that I have worked for seem pretty standardized. I've never seen one with so many different OSs in their network. Typically, their IT departments do a pretty good job of making sure everyone is using the same level of gear, with maybe a couple of outliers.
If you are referring to generic web development testing, then, yes, you do need to test on all of those browsers, even the new ones from Firefox. And you also need to test on Macs with various flavors of Safari and Chrome, and on other Windows browsers/versions, as well, like Firefox 2-3.x, Opera, Safari, Chrome, and even on Linux boxes with FF, Chrome, Konqueror, etc., should your market require it. Then you move over to mobile device testing, where you need to test iOS, WebOS, Symbian, WindowsMobile, etc., and the variety of browsers available for each of those OSs.
So, if you're complaining that (a) there are parts of the emerging standards that you can't use in production, yet, and that (b) the release of another MS browser means an addition to your testing suite, well, that's all part of the fun. No complaining allowed!