It is an implementation of a standard without the standard being defined so other implementations can spring up.
Git, one could argue, is language centralized also, which is technically true. That I don't have an answer for. But I don't believe handing off so much dependence to a JavaScript application fits for me.
A C/C++ application like Git I can overlook, at least for a decade or so, but JavaScript feels like a perpetual beta/prototype only. Granted, that's my subjective feeling.
Raised issue: https://github.com/cjb/GitTorrent/issues/12