as for the "weakness" in a tank like that. Sure you dont often do water changes, but your looking at frequent water testing, and a very careful balancing of the plants/fish/feeding/algae amoung other things. If the whole thing stays in balance, your golden, but if one thing, ie the lights stay on for an extra hour, the whole balance could be thrown off resulting in chaos. Beautiful job balancing the tank, I give him a world of credit, we should all understand our tanks and fish this well!
But of course, water changes are actually natural. It rains, and rivers/streams do drain off. I would also mention that in my weekly tank maintenance, water changes are only part of it, and really, they are not the majority of time I spend maintaining my tank. Trimming back plants, cleaning the gravel, glass, filter, etc take way more time than a simple water change. It seems like he is saving time and effort, but Id bet he spends a lot more time than you think on those tanks.