A friend of mine told me that she had basically used one well written generic paper to get though almost all of the essays required in college because the subject of her paper was so generic and applicable to the field she was studying (psychology). If TurnItIn were to "catch" someone for re-using their own work, I would say that TurnItIn is violating the fair use of the student because it is penalizing the student for being able to re-use previous drafts that were written by the student.

I'm sure teachers don't condone the idea of students re-using previously submitted work from another class, but I think that it is a legitimate right and just shows how ignorant some teachers are who accept papers on generic subjects.

There are probably other specific places where TurnItIn could arguably be abusive of ownership beyond fair use, but there needs to be a specific context to the situation.