He's assuming that the ground's perfectly smooth and flat when in reality, especially in the city, there are plenty of stuff to slip on and grab onto. I did read the 20+ pages there but somewhere he mentions the bike tire compresses so that a light thread essentially becomes a slick anyway? It doesn't, you can see when you ride a bike over a metal plate the parks left by the thread.
Personally I've slipped on the edges of manholes or those stupid metal plates they sink halfway into the ground for construction and have had the edge of a thread grip onto the sharp edge of the interface between it and the pavement. How do I know? Cause afterwards I go home and I can see a patch of the thread where it's worn away.
Just try it, on a real patch of dirty road, which is usually full of grit, dust, sand, etc, spin the wheel and then let it down on the ground, see which one slips the most before stopping. Many people also assume that the threads are to prevent hydroplaning, which isn't always true, it's always nice to have something to lock onto features on the road, once again, which isn't completely smooth and flat.
I have a road tire 700x23 with a really fine pitch thread on it, which gets less traction than a pure slick then. I'm assuming if this guy's right then the smoother my rims are and the smoother my brake pads are, the better they work?