That is the exhaust, not the underbody. It rusts very easily due to the heat and inferior materials used. If it was a stainless steal exhaust it wouldn't rust so easily, but then again the vehicle would cost much more. In a vechile in this price range they should be using stainless steal like the German manufactures do, but I don't believe any of the Japanese manufactures do. This is a Toyota quality that is carried over.
I doubt the dealer will do anything. They will tell you it's covered under warranty and only if it completely rusts all the way through and leaks will they replace it.
