This is the single best article I've read all week on the topic. If you read this a couple of times, you will walk away with a better understanding of this issue than pretty much everyone you know, including many of the people writing about it.
Third Party Browsers Blocked on Windows 8 for ARM? by Kshitij Sobti
This is another really good article that helps to explain some of the "What about Apple? Aren't they doing the same thing?" questions I've been hearing.
Mozilla on new browser brouhaha: Microsoft, Apple different cases by Gregg Keizer