Nitrate is also consumed by algae, and several genus of bacteria have been found in freshwater sediment to utilize nitrate in an aerobic environment. However many of those convert the nitrate back into nitrite. But, poo that works its way into the substrate can be broken down anaerobically eliminating some nitrate.
Another point is that spero has been keeping his set up without water changes for a long period of time. Seeing as nitrate concentrations at 120ppm become toxic to fish, if no nitrate were being removed from the system, I imagine he would see some extreme negative effects on his fish.
I still believe in water changes (as I do them myself). But in mature tanks, I think there is reason to believe that balance is possible.
I am curious to see a test of the nitrates though.