Rx was invented by Microsoft, so C# is a rightful first choice for Rx examples :). That code doesn't demonstrate Rx per se, it demonstrates how lambda expressions, extension methods, anonymous types, type inference enable a succinct backwards-compatible (to some extent) functional syntax in C#.

Look at the type signatures of many LINQ and Rx methods. I would hardly say they are succint. While just using expressions can be compact, maintaining a functional library or creating functional methods in your application will be a chore in c# due to the verbosity of the type syntax (Type inference won't help you on method signatures)