<feckless rant>
Silverlight neither includes nor provides access to any true 3D library. The reasons I've heard for this are
1. they want to keep the download small,
2. there's (allegedly) no cross platform 3D library that has a sufficient install base, and
3. the Silverlight dev team has limited programmer resources, and needs to target (what their marginally effective management thinks is) lower hanging fruit.
I would argue, however, that none of these reasons are nearly strong enough to defend this (unbelievably poor) decision, which has persisted for several *years* now.
The most important objective, by far and away, for Silverlight or Flash or any other Web Widget, is increasing the install base and the developer base. That objective is far more important than any other. Being a small download is a means to that end. Using cross platform libraries is a means to that end. Aiming their developer resources at strategic targets is a means to that end!
OpenGL is a cross platform, true 3D library with an install base that numbers in the 10's of millions, if not 100's of millions, and if either Adobe Flash or Microsoft Silverlight (or any other web widget, for that matter) provided access to it, within 6 months to a year, you would see that number jump dramatically. (How strong is the gaming market in Asia? How strong is the on-line gaming market in general? How often have we vastly underestimated computer users' desire for the convenience, cheapness, and perceived safety of the web browser over other options?)
The OpenGL api is consistent (or plenty consistent enough) across OSX, Linux, and Windows. If you're looking for a cross-platform 3D library, OpenGL is the clear winner. By far and away. Hello, it is the obvious answer. So by saying "there's no cross platform external library with sufficient install base" what they really must be saying is "there's no *Microsoft controlled* cross-platform external library with sufficient instal lbase"! For crying out loud, if we're waiting around for a Microsoft controlled external 3D library to penetrate OSX and Linux - well, which should we wait around for, that, or for hell to freeze over? The world will stop turning, and start going the other way first! I mean, seriously, that will happen when pigs fly out of my bottom and into the sky.
The fact is, there is nothing that could be done to improve Silverlight that would go anywhere near as far toward achieving what has to be by far the most important Silverlight objective as providing access to OpenGL. This would be an easy thing for them to do, if they'd just get over themselves (Microsoft-wise), develop some balls (courage-wise) and give it a shot. If they did, on-line game developers would jump onto the Silverlight platform en masse, and large masses of users would download whatever library was required to play the games.
There is no question that these things are true, they are obviously true. It's time, it's been time, it should've been done at the outset. The failure of the team to even pursue it for all this time is dissappointing, dissheartening, and completely inexcusible.
</feckless rant>