To give some perspective: we were lucky to have less than 2% of traffic coming from IE, most of those visits via IE9+. This made the decision to switch easy in terms for browser support in our case.

YMMV of course but it definitely makes sense to look into your target audience. For some people Firefox 3 and IE6 might still be user bases that are worth supporting, we are glad to have a product for web and mobile developers :)

I wouldn't be surprised if this decision also makes sense for a lot of other target audiences, especially when you consider that you are in it for the long term.