A car handle is treated as part of a conceptual integrated whole car, if you will. It's not as if the frame/chasis arrives at the dealer, who then bolts on components like door handles. From a legal standpoint, the car/bicycle warranty is different.

Now, that being said, the hangar is a grey area. It could have been attached to the frame from the factory, even though it is a bolt on piece of metal. BUT, as has been stated, can one prove the hangar was faulty...or was there bad derailer installation?

I've seen three broken hangars in my time cycling, which is somewhat less that RW. One was when a guy crashed in a crit. The second one was when I was riding along with a friend, and a plastic grocery bag blowing across the road contacted his chain and got sucked up into his derailer, snapping the hangar. (Which, incidentally, is why separate/replaceable derailer hangars were made). The third was a guy pedaling uphill at RAGBRAI...it was a cheapo big box store bike, but he actually was just pedaling along when it snapped. Weirdest thing.