> So should we all just "support the working features" of the lowest common denominator
As the parent and a a person with 16 years (yes that many years!) of experience managing and putting together well known corporate web sites and web apps, I'd say that yes you should.
The web is about being open to everyone regardless of the technical limitations.
I'm confused as to how being a parent is particularly relevant, but anyway...
This particular application is aimed at a narrow category of professionals, none of whom are likely to be using IE, or at least tied to using it. It would thus seem like a bit of a waste of effort to support it, given that it's more troublesome to support than WebKit and Gecko, and also given that Microsoft has promised that IE's standards support will improve, so it'll probably just work on IE10 anyway.
As the parent and a a person with 16 years (yes that many years!) of experience managing and putting together well known corporate web sites and web apps, I'd say that yes you should.
The web is about being open to everyone regardless of the technical limitations.