Both engines use the same gasket design.
The one in front of the cat has nothing to protect it in case of a overly rich condition or coolant burning in the combustion chamber or any of a number of things. These things can foul a O2 sensor pretty quickly.
The rear O2 sensor is sitting behind the cat (because its job is to monitor the cat's performance) so the cat takes care of a bunch of the nasty before it reaches the sensor.