The 72 browser versions thing is an exaggeration. For your websites, add this tag: <meta http-equiv="X-UA-Compatible" content="IE=edge" /> - and you force IE to use that version's latest documents mode. So good point about IE's slow adoption, it really is annoying and holding back the web - but for your websites, you can easily force the document mode of your choice, avoiding the crappy emulated modes.
Absolutely. That line is critical to avoiding pain. Library authors don't have that option, unfortunately. :/
But even if we ignore the compat versions for now (and quirks mode (and almost-quirks mode)), we still end up with up to 10 IEs in play simultaneously.
"Edge" rendering on X browsers is still X different ways for all those stuck-in-time browsers to decide what "edge" meant at the time of their release or last update.
That meta tag is a good practice but not the ultimate solution.
