Given the lack of question mark in the thread title I did wonder if this was a question or a proposed economics thesis title.
Where the land gets incredibly murky is whenever you have a codeshare. Imagine booking on United but operated by TAM, your AP miles are determined by the TAM fare class which will be determined by how UA fare classes map to TAM fare classes and pretty much nobody knows that part of the equation, certainly not front line airline reps or the huge majority of travel agents.