Filezilla on windows assumes sftp to be SSH transfers. So I think you've got that backwards.
What, exactly, do you think I have backwards? I just tried to explain how wildly diverse the meanings are, and how people use the terms. I don't care what your favorite FTP client means when it uses the term SFTP (bully for you, that you happen to use one that uses the term correctly)...I'm telling you that there is little agreement in the wild about what the term means, and many people use it incorrectly to refer to FTPS (and other kinds of secured FTP).
Googling SFTP is actually very heartening--it takes quite a lot of searching to find anyone using the term incorrectly. This wasn't always the case (and the hearts and minds of the non-technical masses takes a lot longer). We still see at least 50% of our customers saying "SFTP" when they mean "FTPS" (and we don't support any of the proprietary FTP-with-encryption protocols).
I think part of our users confusion comes from the fact that the server that provides SFTP service is called sshd and the server that provides FTPS is called proftpd. Obviously, FTP is right in the name of one of them, so that's where all FTP comes from! System administration is hard.