In terms of WebGL though, I think the major platform for it is the traditional Desktop OS. When people talk about creating WebGL MMOs with 3D graphics, etc. I think there's too much of a performance-bottleneck in terms of graphics for WebGL to be hugely popular on phones. If this was the case, Microsoft would still have the home-team advantage, and the ability to set the tone for future web graphics APIs. They did the same thing to the console market: when they came in, OpenGL and fragmented proprietary APIs dominated the market. Post-Xbox, DirectX became the first-class API for 3D game development. I think we could well see the same thing happen with WebGL if Microsoft makes a move to do so. And at this stage I can't see any other reason for them to hold out for so long in implementing WebGL in IE, unless they plan on subverting it.

That said, Microsoft didn't create a competitor to canvas and many other new web APIs (but I don't know how standards-compliant they are these days in terms of Javascript, Canvas, SVG, etc.).

WebGL would have to have a killer app on mobile for Microsoft's lack of mobile presence to hurt them. Currently all WebGL Demos I've seen have assumed a desktop-level of graphics performance, and no phones are "officially" capable of WebGL yet.

I just tried the three.js examples from my Galaxy Nexus (running 4.1) and couldn't get any of them working in either Chrome for Android or the default browser. That said, I know it's possible with some hacking and tweaking. From what I hear iOS has about equivalent support at this stage. That said, Apple and (to a lesser extent) Google could roll out this support pretty easily in an update, but I maintain my initial reservation; that phone hardware will not be performant enough to make WebGL a viable replacement or complement to native OpenGL development on those platforms.