I suppose the thing I find irritating about this is that industry leaders (excepting Microsoft, of course) use platform independent testing software. Cisco in particular used testing software on its Academy website which worked great for me in Firefox on Debian Linux. Is it really that much more cost-effective to use Windows-dependent testing software on a website?
I think many web developers confuse popularity with standardization. Nobody works hard creating a web application in hopes that it won't be usable to a segment of the population. They write the app assuming that you will be running Windows with IE, as they see this as a standard and not an option. They only choose proprietary languages and so forth because they aren't even aware anything else exists. I work with a bunch of programmers who don't seem to realize that there is such a thing as software created without Visual Studio, and I'm sure whoever developed this web app has similar views. Welcome to monoculture.
--Jestin