I tried to create a whole new project and it's fine if I follow exactly the blog page you gave me.
I don't know why, but it seems the architecture has changed from when I installed my Ionic app.
Previously (on my version), the "app" folder and its containing folders was inside the "www" folder.
It looks like now the "app" folder is on the root of any new ionic project.
I guess I'll juste have to tweak around and copy/paste files and hopefully it's gonna work eventually...
EDIT : updating to the newest version of Ionic finally solved the problem.