Usually its only the really crappy $tealerships that beat you up on warranty claims for not having oil changes done through them. Receipts, unfortunately, don't mean anything. All it means is you bought the oil/filter, its not proof that you actually used it on your vehicle. Many dealerships will tell you that.
Honestly, one look inside the engine and they can tell whether you've changed your oil regularly or not. Usually its just a way for the bad ones to weasel out of performing warranty work.
Believe it or not, legally speaking, I am pretty sure its up to them to prove that your "lack of maintenance" damaged the vehicle and voided the warranty. Some will try to do it backwards, and act like its your responsibility to prove to the dealership you maintained it, but not legally so (by an act of congress, no less).
I have always done my own maintenance; oil, filters, greasing zerks back in the day, etc. I've never had major internal engine work done under warranty, but I have had a water pump replaced on the wife's Grand Cherokee, and the manifolds replaced on my truck. Never a word about proving maintenance.
