Oh, but you can have mutable state in different parts of a program even in a pure FP language (without having to jump through any hoops, it's right there and pretty easy to use), although a processor or signal simulator may benefit from things like FRP that are a lot better suited for, well FP, then imperative languages.

But I actually wasn't asking about pure vs imperative, but rather FP vs OOP. I haven't heard of a pure OOP language, but in that context I think those properties could be seen as more or less orthogonal.