Given that so much software requires installing the JVM, or CLR/Mono run-time, or widget toolkit, or even is specific to an operating system, is it really that much to ask that users install a certain browser which literally runs on any OS, is free and open-source, and can be installed in seconds/minutes?
Why do we rail against people for using the wrong OS, make people dual-boot and run virtual machines, yet installing a different browser is completely unacceptable?
No one minds that so many apps are iOS/OSX/Android/Windows exclusive, but when web-apps don't run on IE it's a problem...