I don't know Fetchnotes and Simplenote, but I use another tool for the same purpose that seems to meet all your needs: it's called evernote.
I need to be able to sync my notes on my Android cell phone and
There is an evernote webapp that runs in your browser, an app on android/windows/mac (and even linux http://doc.ubuntu-fr.org/nevernote)
I need to be able to have the actual files, not only to view and edit via UI.
Evernote is "note" centered (dah!). It's a notebook. But you can attach all sorts of files to them, including audio files & photos (even when recorded/taken directly through the phone app, very handy!)
Plus, it has this web clipper that makes it super easy to grad stuff on the internet an store them in one of your notebooks, putting in some tags on the way.
On computers, ideally I should be able to edit the notes in Emacs, but
not only on the website in a Web browser. This probably mean there
should be a Emacs mode for the note system.
Okay, now is the BEST PART :) it has an awesome command-line tool that runs on linux, called geeknote.me. So basically you can create/edit any of your notes and send it in the could with any editor (but it works better with vim, like everything else, nat(u)rolly ;)
That's the only tools I have used, so maybe there are other good tools out there, but I can definitely recommend the one.