I pretty much assumed this would eventually come, whether it was a resignation, a forced resignation or a firing. The simple fact is that further up you get into a company, the less you're allowed to say because people start to believe that you are a full fledged representative of that company...which you technically are. The old saying fits with corporate methodology, though in a slightly more metaphorical manner: 'Loose lips sink ships'. And he hammered a big damn PR hole right in the side of the U.S.S. Microsoft that needed to be plugged.
Whether he was joking or not is completely irrelevant. Whether he has a family or whatever is also irrelevant. He caused problems by making people angry over a controversial theory about the next X-Box and he kicked the hornet's nest. His job was the casualty.
What still amazes me is that people don't realize that this happens ALL THE TIME. I personally know three people who have been canned because of the stupid things they did online. One did a naked photo shoot when she was nineteen years old. Seven years later, things surfaced, got around and she got canned for it. She happened to work in a government office. Two others involved bad mouthing the employers on Facebook and it got back to their bosses. Simply put, online does not mean 'free pass to do things' any more. These days, it's pretty standard issue to keep an eye on these things and deal with problems as they come up, because PR is huge.