An interesting point, although I think that's only relevant if the documentation lists the ABC and a reference to it.  (python-3 doc essentially does this.)

I see no such reference in the 2.7 gzipfile doc, which leads me to believe, (from the doc alone), that it's an independent implementation of a "file like object".

This may not be important enough to even merit the time we've already put into it.  Please feel free to close this ticket without change if you prefer.