There are also things like JAWS screen readers and other add-ons that educational institutions MUST use to comply with ADA regulations which, surprise, generall

There are also things like JAWS screen readers and other add-ons that educational institutions MUST use to comply with ADA regulations which, surprise, generally depend on specific versions of IE to function (though personally the ones we use at my work are at least compatible with IE 8). There's not really a very good alternative to this-- Firefox has a history of breaking it's extension model with every major version, and Chrome is still in relative infancy (though I personally use it every day), so I think it's understandable that "enterprise" software companies haven't rushed to ditch IE for them.