Sounds like you have your answer. There are different grades, sizes, colors, etc. There is overspray clay that is meant for removing more than just the standard IFO that normal clay removes. That stuff is more abrasive and rougher on your paint and usually not found on the shelf at AutoZone. I've seen Meguiar's version of it and Clay Magic's version. I'm pretty sure that Meguiar's uses a different type of clay than Clay Magic, but I can't remember for sure. I don't do the kind of detailing that would require it anyway, so I don't worry about it.
You'll have to do some research on the different types of clay. From what I remember (and my memory isn't great) there are two types of clay made by only two companies. Everybody is selling relabled versions of those two clays. There isn't anything shady about it, that is just the way it is. Who uses which clay is something I don't know. From my experience I would say that Clay Magic, Four Star, and Mother's are using the same type. Meguiar's seems like something different, although I do imagine that these companies make different qualities of clay depending on the requirements of their clients.
Again, this is all what I remember reading a couple years ago. I don't know if the threads are here or on another board, but I know the lawsuit information is out on the web. Maybe someoene else can pitch in and clarify my hearsay. lol
