1 Nitrification is an acidifying process, the conversion of ammonia to nitrate leafs excess H+. overtime pH en alkalinity (KH) will drop. Water changes are there to restore those values.I'm not so sure about that. About 10 years ago when I first started in this hobby I had a 4ft clear-seal for about a year. It was chock full of plants. No co2 or anything until I started to try and grow HC towards the end. Anyways, After about 3 months when the plants had matured I hardly ever did a water change, and I do mean hardly ever and the parameters were pretty much 0 all the time. So I do think its possible, with a big enough tank, the right light and the right stocking that you could let nature get one with it. How, I have no idea as I will admit that this near perfect balance I achieved was pure luck and I have never managed to do it since.
So I don't think people are stupid or lazy or an idiot to try this approach as it is obviously possible. I just don't have a lab to set up umpteen tanks and try numerous things to try it again.
2 we can only measure so much, we have a handful of mostly indicative tests. Water quality is also about all kinds of other stuff, organic waste etc. Those who measure EC or TDS know that no matter how much plant growth, EC/TDS will always rise, more and more solids get dissolved, it may go reasonably slow, but will never stop.
It's not a law to do lots of large water changes, and your tank and fish may still do ok if you don't change water for a few months. But water quality will go downhill without a proper water change from time to time.