http://forum.unity3d.com/threads/83071-Unity3d-plugin-for-embedding-webpages-on-WINDOWS-is-ready!/page5

Originally Posted by Retronamic View Post
Is this Windows .exe build only? No webplayer support on Windows?

Yes, UnityWebCore introduces Webkit engine into Unity. WebKit is
developed by native C++. So there may be less possiblity to port
to Unity webplayer

あぁなるほど…unityをwebkitと統合するためのUnityWebCoreというのが
あってそれはC++で実装するので、webplayerは凍結する方向で動きたいと。
C#実装だったのねwebplayer。