One of the problems here is that C# and F# interop isn't always as easy as the article implies. F# has a lot of types which, when exposed in a public API, are ugly as sin in other .NET languages.
That issue is not F# or C#'s fault - it's a limitation of the expressiveness of the CLR's type-system (it doesn't support higher-kinded types, varadic type parameterization, or non-typename type parameters).
The hope and the expectation is that the CLR will gain support for first-class representations of F# concepts to allow for greater interop with C# scenarios, but the CLR's development has always been tied to C#, with other CLR languages like VB.NET and C++/CLI only exerting minor influence on the CLR's design with most of their language-specific idiosyncrasies being handled by library-code and compile-time tricks instead (e.g. VB.NET's "On Error Resume Next" statement is implemented by having the compiler wrap each individual statement in a try/catch instead of having the CLR specifically support it (though in this specific case that's probably a good idea as OnErrorResumeNext is a horrible idea I'm sure we all agree).
Minor correction, only Managed C++ and C++/CLI have the full power of the CLI, many of the performance improvements in C# have been related to exposing those MSIL capabilities to C# as well, which before required generating bytecode directly.
Which is kind of ironic given how they usually leave C++/CLI out of the picture, including the cross platform story.
