I love that he openly defied them, but I also hate it. It's both good and bad.
On the good side, yes, I agree that from what we've seen Windows 8 is a step backwards in terms of openness, leaning more towards the Apple "closed platform" that I hate so much. I think it's a good sign that Microsoft is reaching out to help - albeit the most profitable one ever - an indie game to certify. But that begs the question of why should you need to certify anyway?
But on the downside, it shows a disregard for his fans on Notch's part. (not to mention rudeness! sheesh) Minecraft is his baby, sure, but I'm sure there's a lot of people who play it who might also want to use Windows 8 without having to maintain more than one OS. It's basically a big unwarranted "forget you" to those people, whoever they are and however many of them there may be.
Then again, I think the whole certification thing is a guarantee of performance, not a requirement to run it on the OS. If it's the latter, that's a whole new height of gigantic-loving-mistake for Microsoft.
forget I'm a quality poster
seriously just
damn I'm good
don't you just love me