This isn't unique to cars. Customers try to get one over on companies to avoid paying for their mistakes ALL the time. Not just car owners towards dealers. If you had a warranty on your windows, and your kid broke the glass, are you gonna call and tell them your kid broke it? Or are you going to say I came home from work and noticed it was broken, I don't know what happened, please replace it?
I've been in customer service for 18 years and it would amaze you the lengths some people will go and how often I see it. My guess is the vast majority of companies, including ones the size of VW and the company I work for, are not suing their customers for anything like this. Burden of proof falls on the company, and they have to be good at sniffing these out. But they won't get them all, and that's a sunk cost that's factored in just like everything else. Plus they don't want to build a reputation for being the company that sues it's customers.
Car people have been trying to get warranty work done on modded cars with varying degrees of success since car culture became a thing. This is not new and no one is getting in real trouble (at least not 99.9999% of people like you and me).