this is kind of unfair. the lessons microsoft and the development community have learned from working on browsers were all things that the Chrome team gets for free. they also get to start from scratch, whereas the IE team has to work on an outdated codebase and provide lots of legacy support.
Microsoft is free to rewrite IE from the ground up any time they'd like. The only legacy support they need is the same specifications that all other browsers are supposed to adhere to.
There are APIs for browser extension that Microsoft will want to continue to support as they are no doubt used by partners/corporations. It's not just about how well the web renders. The same way that firefox would be unwilling to start from scratch without providing support for the present plugin framework.
