You're absolutely right on that, there is no other way of differentiating a quality paint from a lesser quality paint...but it's the same for most things isn't it?
Good quality paints have around 20 ingredients in them and many of those come in a number of quality grades themselves so it's a complex mixture for sure; but the price also reflects research and quality assurance, as well as the equipment they use to produce the paint in the plant. And the successful paint companies are the ones who are visited the most often by resin manufacturers, who present the best they can offer too.
The generic manufacturer buys ingredients on price to satisfy the price parameters of their clients and therefore don't get the advantages of the millions of $ of research the companies like Rohm&Haas put into their resins, all of which is meant to produce a better paint.
The beef a lot of painters have is directed at consumer providers, say a big box store, who specify a generic paint at a given price level, then load that price up with admin costs and pretty head offices so that the buyer thinks he's buying a quality paint. But in fact they're buying an $8/gall product.
I guess there's nothing wrong with that, but what effect is that having on BM, Sherwin-Williams etc? It's all that is wrong with a consumer-driven society that we have.