What actually happens when you send a unit in to Apple itself for repair can vary. In some cases Apple will simply ship you a completely different computer than the one you sent in (different serial number, specs, features).
They can then take your unit and break it down for parts or even fix it up and resell it (whether they resell any/all units sent in for repair and not simply returned working computers I don't know I am merely speculating).
I believe, based on service tech documents I have read, that Apple always replaces an iPod with a different iPod unit when sent for a repair no matter what. It really isn't worth it for Apple to stock *extra* parts for service when they sell so many in retail already far outstripping existing production. That and the components are not really fixable due to size/design.
If what you get back is in far worse condition, raise a fuss over it. But if you get "add-ons" I'd keep my mouth shut, as long as the whole computer worked and wasn't all banged up and such.
Your response should never be "I'LL SUE!" as that just makes it harder for the rest of us to just get our computer fixed and be done with it with even more conditions and clauses and hoops to jump through thanks to endless lawsuits.