I was curious why C++ isn't offered as a code-behind language for ASP.NET applications?
If you are interested, here's some interesting articles about how you could use managed C++ as your code-behind:
Most ASP.NET applications run in limited trust modes. And C++ generally compiles into something that requires higher trust levels.
C++ is supported, but as another answer says - most C++ apps require a higher level trust mode that ASP.NET cannot support. You can, however, use C++ to create assemblies and web components that can then be consumed by ASP.NET & IIS.
I do not have the answer. However for hardcore c++ guys who want to develop ASP.NET apps in C++, you can always build your core logic etc in a separate project/assembly. You can't run away from VB.NET or C# totally though.