Ya I am always very happy with this dealer. Seems to actually care about me as a customer! Shocking I know. I wondered the same thing, however they did (claim to) check the sensors (I believe with their diagnostic tool) and they determined it was the cat. Could have been the sensors though.
Apparently NJ (I read this on another forum) starting in 09 has a longer warrenty on cats. Not sure if that's accurate or not.