IE's been a solid HTML5 browser for a couple years now. As good as Opera or Safari, certainly.

Not really. There aren't regular updates to IE adding new functionality from the living HTML5 standard (and other standards). Further, the latest IE cannot be installed on some older, yet still popular, versions of Windows. These two factors combined means that a lot of people don't have a modern up-to-date IE.

The current update frequency for IE is a dramatic improvement over older versions.

The fact that you can't install IE11 on Windows 2000 is irrelevant. I can't install Safari on my Windows machine anymore either, and it's still a HTML5 browser (albeit a bad one, the last time I tried it on a Mac).

Users not installing updates isn't relevant either.

IE is a perfectly respectable HTML5 browser. It runs my HTML5 games better than Opera or Safari and has fairly comprehensive support for non-bleeding-edge features, especially if you look at 11 (coming out soon, I believe).

> The current update frequency for IE is a dramatic improvement over older versions. Obviously an update frequency of 1 year is a dramatic improvement over an update frequency of 5 years, but still is not enough. Basically it means "if a feature is not present in IE11, wait a year, or two".

Microsoft clearly did not make IE a business priority to the extent that Google has with Chrome, and obviously Mozilla with their flagship.

Whether or not they could do better is separate from the question of whether it's a browser that can handle modern sites and applications. It can.