In the paragraph you mention he's referring to used chains with other lubes and dirt on them, it's just a bit of hygiene to at least clean those before you dunk them. I replace the wax in my cooker every 4-5 months, across 7 bikes and I live in a very dry climate, and in that time even only with cleaned/waxed chains the wax mix will get pretty grubby.
WRT the new KMC chains, I just thought I'd give it a whirl and see what happens - already use the wax method, never used the KMC chains before, thought I'd try it out. Seems ok so far, if I have to bin the chain prematurely I'll let you know.
One thing I will say, this may point to my poor maintenance habits previous to waxing, but on my road bike I noticed a huge dead spot in the top of my pedal stroke after I'd waxed the chain, my freewheel would tick when my foot was coming across the top.