The CLR is a language-neutral platform. So naturally, our debugging API (ICorDebug) operates at the IL level so that it can be language-neutral as well. The Edit-and-Continue support in the debugging API is language-neutral, though it was mainly designed to ensure that key VB scenarios worked.
In theory, any 3rd party could write their own managed debugger and support EnC for their own languages ([Update]: see here for how a 3rd-party can support EnC). The C# team put this to the test because they did EnC without any additional modifications to ICorDebug.