Most of the time, people say "slash" and it's boyslash they're talking about. Most of the stuff listed as "slash" out there is only of the m/m variety. The f/f slash gets drowned out by the sheer torrent of m/m that's out there.

So when you say "it's slash to me whether it's guys or gals," most of the people out there that regularly write femslash presume they're not included. Femslash has a whole different set of conventions and vastly different big fandoms than boyslash.

Calling it "slash" is more exclusionary of femslash than inclusive of it.