As you found, and as you probably expect, the official answer is "this has nothing to do in a media library"
But this is subjective, so really should be "
Laurent defines what should or should not be part of sfml". For example, when you say
multimedia, I think of video, but sfml doesn't support loading video files, and nor do I want it to, but I'm just saying that 'media library' is ill-defined. Even I would say Networking doesn't fit under the 'media library' definition, but is a useful component nonetheless, just like a simple cross-platform file/directory system could be.
Many users would like to see SFML as a framework that they can use to build any program. But SFML is not that. It's just a multimedia library. Don't be afraid to use other libraries; in fact I don't understand why people don't want to rely on multiple libraries to create their programs.
I think a lot of people come to SFML because it is simple and clean, and possibly because they are also just learning how to build graphical programs, which is supported by the nice SFML tutorials and prepackaged binaries for msvc/xcode. So when these people want to do a simple task that isn't supported, suddenly they have to go and find a library to do that thing, which may require using an API which isn't simple, or even (gasp!) compiling the library, which on Windows is especially difficult to do if an msvc project isn't supplied. So I don't think its a case of "don't want to rely on multiple libraries", rather than, "have difficulty using other libraries".
In any case, I'd be interested to hear what the majority of SFML projects were, and how their requirements match up with the feature set of SFML.