Hi Dwarden,
I cannot deny there is a link between market share and number of infected. But only if there are malware vectors = possibilities aka vulnerabilities.
Now this is not so with Apache versus ISS = 80:15, still Apache has been many times more secure than ISS over the last couple of years. Here your assumption seems to be false.
Only when you use a plug-in to functionally start-up MSIE, you will hit the jackpot. Also from within for instance firefox.
Couldn't it be, that when IE was developed security was not a big thing, and the number of features only grew and grew?
Just consider this funny example and you have to admit the case IE versus alternate browsers is a little more complicated, as you like to assume or what suits you better:
http://blogs.zdnet.com/threatchaos/?p=311greets,
polonus