Kirk, I think that's a little misleading. Catalytic combustors do not need to be replaced regularly if they are used correctly.
You cant add wood to them till the charge is fully down to coals, and the combustor has cooled. Adding wood while the combustor is hot will cool it rapidly and damage it.
Start up procedure is important too. You need to get the fire hot and the combustor active before you close the bypass, or the element will become dirty in a hurry.
You have to pay attention when using cats, buy they work very well.