Hello and welcome to the forums [member=Alain].
Well, I must tell you a big secret! Most of the times, if not all of the times, things are not the way they seem to be!!!
In a more serious way, the models are actually, used and without them the libaries won't work!
Let me explain a bit more.
For example, on the very first example, the simplest example, the creator says:
"Even if you are bored to write the set_table function , the library searchs if the function name exists as a table name"
This wouldn't be possible if the grocery_crud_model.php didn't exist!
And the story goes on and on..!