Having skins on your iPhone doesn't void the warranty.
Agreed, but there is always a slim chance, if you have been excessive and careless when applying skins with a solution, that you may trigger one of the moisture detectors via a stray drop or two... thus voiding warranty if they check the detectors...
I did this on my 3G, but never had a problem with the phone, so never came into play for me. Did bug the hell out of me for 6 months until the warranty period was up!
Moisture detectors? You're kidding, right? Most phones, it works or it doesn't when it comes to moisture. You mean to say they have some mechanism that records whether moisture invaded the phone, whether it has caused malfunction or not?
Wow where have you been? Moisture sensors have been in cell phones for a very very long time.
A moisture sensor is simply a sticker inside the phone that has ink on it that will streak and smear when it gets wet. It's nothing too complicated.