Dropping support for older browsers shows why Google Apps will continue to struggle against Microsoft products for government contracts such as was the case recently in San Francisco. Large organizations get locked into legacy OS's for many reasons - example government agencies who bought and rely on geospatial data in Autodesk Mapguide format.
Luckily Google has decided that the entire rest of the world doesn't have to wait for every bureaucracy to upgrade their antiquated systems in order to make progress.
At this point MS want IE6 (and 7) to die as much as everyone else does, as it has become a source of embarrassment.
Even MS's own online office applications don't support IE6 and have not done so since the back end of 2009 (see http://blogs.msdn.com/b/officewebapps/archive/2009/08/05/985... for confirmation). Not supporting IE8 would be a problem (a number of our banking clients are in the process of transitioning away from IE6, but unfortunately only onto IE8 and I assume many government bodies are in a similar position) which is possibly why Google have drawn the line there, but if not supporting IE6 is an issue then Microsoft's online products will be affected as much as Google's. IE7 is pretty much moot in my experience: I don't know of any environment that upgraded to 7 which stuck with it, those that stuck with IE6 are either still stuck there or are upgrading to 8 or something more modern and those who moved to 7 have moved again.
http://en.wikipedia.org/wiki/Mapguide
http://usa.autodesk.com/adsk/servlet/item?siteID=123112&...
And yes that is a plug-in for Netscape that is still available!