This looks to me like Microsofts way of putting their fingers in their ears and going "lalalala I can't hear you".
Did anyone, ever, really believe that Microsoft were going to back WebGL in any form or fashion? I sure didn't. If they did they could have chipped in and said "We know there are security issues, and we want to help fix them."
This sounds really weird when most of us, including myself, sit on Windows systems, but why do we let Microsoft bully the entire web industry? I'm gonna say it again, we all knew they were going to try and push their own proprietary solution, instead of supporting WebGL. If everyone just waited for Microsoft to come along it would a) be futile because they won't and b) reinforce the idea that they control the market. Neither are good things.
I'd liken it to releasing a game made in Construct Classic. I posed this question to myself. "If I released a game made in CC, I could only sell it to Windows users. Would that be profitable?"
So I thought about that. There are three major OS'es. Windows, Linux and OSX. I know few games released on Linux. I know fewer people that actually game regularly on Linux systems, and even then it's mostly homebrew and emulators. So Linux didn't seem like much of a loss.
What about OSX? Sure there are games to be had on OSX, but again they are few. If you bought a Mac you most likely didn't buy it for playing games. Going by that reasoning (which may very well be faulty, I'm no market analyst) I concluded that going Windows only would not be as bad as I originally thought. Not ideal, but a calculated loss at the least.
Doing the same thing for browsers. The big ones are IE, Chrome, FIrefox and Safari. Of those four, IE is the only one without WebGL support. Microsoft likes to tout how big of a userbase they have with IE. They neglect to specify that the majority of that userbase is IE6 and below. And of that a substantial amount is companies using it on their company computers. Looking at it that way I'd say that IE would be a calculated loss for WebGL developers.
Let's just ignore the big internet bully!