I never seems this argument when you install after market car parts and install the parts yourself or your neighbor or some random car service, if you changed your lightbolb in the car and the engine breaks 1 month later you can't void my engine warranty. When I install a cheap battery, the pone burns and I bring it to warranty then the warranty people can photo the phone, show the problem, show the faulty battery and I am at fault.

If you are concern that evil people are out to get Apple, those evil people have many other ways to do it, there is no good reason to screw 99,99% of your user because some random guy install a cheap battery and then puts a photo and rand on the internet, that does nothing, there was a need for thousands of people to complain about the keyboard issues before most(but not all) of Apple fans believed that Apple could make a mistake(so a few rants won't have any effect).