Putting your phone in your back pocket and sitting down is in the same class of abuse as jumping into a swimming pool with your phone in your pocket. I would never expect any phone to survive either.
(unboxing Z3 under water)
Not until now has putting a phone in your back pocket been "crazy." I recently upgraded from the iPhone 4 (which I had for 3 years) to the 6, and for the life time of iPhone 4 I've sat on it for extended hours and had it my back pocket. I currently do the same with the 6.
What I really think has happened here is this whole thing is being blown out of proportion because 1.) its Apple and 2.) they moved 10M units in a weekend (if they had 1% defect rate, thats 100,000 angry tweets, status, youtube videos and blog posts).
FWIW the only videos I've seen of the phone actually bending are the non-measured ones when someone applies an inane amount of force with their hands trying to destroy the thing (with an Li-On battery inside!)
There have been other situations where I have unconsciously put my phones through pretty intense pressure, not realizing it was under me where I sit down or sleeping with it and it getting stuck in between mattresses/cushions/pillows whatever (although for other reasons I have been trying to not go to sleep with my phone anymore, leaving it plugged in somewhere else).
I think it implies being stuffed in pockets and left in the car (barring perhaps the most extreme climates), and perhaps certain types of drops, but not being sat on.