Course the way I see it, is that corporations probably won't bother for two reasons.
1) Once an in house app is created, they usually stick to it til it can no longer work.
2) Most companies don't want you browsing the sites that would have the issues to begin with.
You're right. Corporations and Govt agencies don't bother because they have massive infrastructure with slow as fuck update cycles. Security issues, should they arise, can be dealt with efficiently. These are the kinds of places where your email and web activity is monitored and where most are prohibited from surfing anyway. Our customers aren't likely coming from these places, but there's still a % that can't be ignored.
The second scenario of course are people who are using pirated copies of Windows. Windows update doesn't work for them with the whole Genuine Advantage thing MS is pushing these days so they never get told to update to IE7 or now IE8. This group is, unfortunately, where a good deal of customers might come from as there are probably more illegal copies of Windows being run that legit copies, especially in developing countries.
You're not very good at estimates and should avoid pulling numbers out of your ass. MS hasn't had a huge advantage in the browser market share for ages. FF is king and constantly gaining, currently estimated at 47.9%. All versions of IE add up to 39.4% with IE6 making up 14.4%.
Browser Statistics
Exactly. Determining the browser you want to support all comes down to what kind of site you are designing. There's absolutely no reason why you can't get simple landing page designs to work in IE6 with pixel perfect results. Once you've learned about the half dozen or so major CSS design bugs that plague that browser, identifying them and squashing them is child's play.
