It's pretty tough to make a tutorial for literally everyone. Heck, some people use CoffeeScript and some use JavaScript, and any of them might be upset if your tutorial uses the other.
If someone wrote a plain Ember tutorial that just assumed the backend API already existed, just as many people might make the complaint "if you already have a backend, I'm sure this tutorial is just great, but for the rest of us..."
If someone wrote a plain Ember tutorial that just assumed the backend API already existed, just as many people might make the complaint "if you already have a backend, I'm sure this tutorial is just great, but for the rest of us..."