Not coming to Hurc's defence, BUT a partially plugged exhaust CAN cause engine temp to go up. The reason the exhaust has lost 1000 degrees is because the water jackets and other engine parts have absorbed all the heat. However, once it gets plugged a bit worse, the engine does not get enough air-fuel mixture to produce enough heat (or power) to do much harm.
A previous responder mentioned something about 1996 and newer vehicles having temp sensors at both ends of the cat. This is not correct. The have O2 sensors at inlet and outlet - and if both sensors read the same the computer knows the cat is not functioning.
Also, someone mentioned the switching from rich to lean - and intimated that was required to allow the cat to work, because one part of the cat (oxidizing bed) required a rich mixture, and the other (reducing) required a lean mixture. This is also wrong.
The catalyst DOES require a relatively rich mixture to function - but the switching back and forth from rich to lean is due to the non-linear nature of the O2 sensor. It can NOT determine the actual oxygen content, but knows if it is too rich or too lean. It switches between rich and lean to get the proper average mixture. There are a few vehicles that use a linear O2 sensor, and the mixture on these vehicles does not fluctuate. The Civic VX was one good example.