Got my iphone 7p on the 1st week, noticed some small debris in the lens, went to my local Apple Store, they had the same device ready in stock as a replacement, in&out took 10 mins. (note my device is probably one of the most wanted one, Unlocked-128 black)

I broke my 6s+ the 2nd day after release and got it replaced the same day. They have separate replacement stock even at launch.

When the first iPads came out, I actually received mine by post a day or two before the official launch day. It worked for a few hours, then the screen wouldn't switch on. At that point, iPads were super rare. Rarer than any iPhones have been since then.

I went to my local Apple store on release day, showed them it wasn't working, and they swapped it out straight away, no questions asked.