I'd love to be able to stop supporting IE 8, the gap between 8 and 9 is almost as big a jump as 6 to 7, but I don't see that happening until Windows 7 support is no longer offered. Windows 7 came with IE 8 preinstalled and no automatic updates from that to higher versions. People are still buying Windows 7 machines.
Dropping IE 9 support isn't even on the horizon for me.
N.B. The company I work for sells to US k-12 schools.
I think the thing is that there is forgotten and hated windows vista, that can update only to IE9, thus leaving it as smallest common denominator after XP end of life.
I think (hope) most people are making those decisions based on actual analytics data and customer needs versus maintenance cost. I still get a fair bit of IE7 traffic, and there hasn't been a "good" reason to run that for quite a while.
Dropping IE 9 support isn't even on the horizon for me.
N.B. The company I work for sells to US k-12 schools.