You are right, it is an apples to oranges comparison. I'm sure there are cases of academic full rides being able to transfer to another school and land another full ride, but there is generally less motivation to do so than for an athlete looking for more PT, exposure, etc.
The main point though is it doesn't make sense for your letter of intent to limit you from looking for a better opportunity if things aren't working out for you. And I don't think that alone really does all that much damage to the already thin facade of college sports being a mainly academic and not economic endeavor. I don't think that will change graduation rates much.