I can speak to this a little bit, actually.

Chartbeat has never supported IE, which as you say sounds like cutting off a major part of your market. Even moreso when you consider our customers which include pretty much every major publisher in the US. However what we've learned is that if your product provides enough value, people have no problem installing Chrome or Firefox or whatever.

To this day we receive pretty much no requests for IE support at all, which enabled us to build a product with heavy HTML5 (mostly canvas) and CSS3 usage.