Of course, if they had bought privacy protection it would be the same situation. But these people don't pay for privacy, they've just got bogus info.
Sure, they're worried about spam, but my registration information for most domains is totally public. Yes, I get spam every day, but it's manageable, especially with a spam filter. Having put my email "out there" and experienced the problem, I don't think that's an adequate excuse.
So. People shouldn't do it, I guess, but is this the same as saying "people shouldn't eat fries?" everyone does it anyway and the world doesn't end.
Does it matter?
Should we report these, or live and let live?
Does reporting it do anything anyway?
let it go.
added: I have reported one domain, but not -exactly- for fake whois. it was for no whois info available whatsoever. the whois lookup for the registrar of that domain would not return any information. it would say something like "too many connections. try again later." after getting this response several times, I reported it. it was working properly a week later. fwiw, that registrar's whois would work properly for other domains, just not the one I was interested in. so it was maybe a missing or corrupted file or something.