I'm curious to know who else out there is noticing this with their iPhone and, if so and you've contacted Apple for assistance, what sort of response did you receive? Was it handled under AppleCare, did you have to send it in or was a replacement provided in-store, etc?
I haven't noticed the same yet but depending on the person you speak with at AppleCare, the response can be somewhat different but there should be no question about something like this being covered under warranty so give them a call.
I don't believe iPhones continue to be automatically exchanged on the spot at an Apple Store regardless the problem or problems as was initially done within the first 14 days after the purchase date and doubtful any Apple Store can repair such a problem on the spot.
So your iPhone will be sent in for inspection, testing and repair or possible replacement with a refurbished or new iPhone which is at Apple's discretion. If you ask nicely, you may be able to get the $29 fee waived for a loaner iPhone during this process.