If you take a look at netmarketshare, there are some scary statistics:
Web Browser marketshare shows IE 9 usage at a little under 7%, and IE 8 usage at a little under 14% (this is probably everyone still using Windows XP). In fact, if you add in IE 10, that's 25% of the web traffic on old versions of IE. That's a lot of people.
Still, the church is doing the right thing moving forward and not providing support for the older versions. It's expensive to support all those older versions. I'm sure the church is deciding where best to spend limited funds, and, unfortunately, that does affect some members. Even with JavaScript frameworks that try to abstract the browser differences, you still have an expensive testing effort to make sure it works. Home users on older operating systems generally can install Chrome or Firefox and be able to use the church tools. It really comes down to employers who don't upgrade systems. Usually this is because they built apps to work specifically with IE and it's expensive to rewrite them to use newer technology.