1: Have you asked them if that actually is true, or read about it somewhere? Or is it just a guess? If they were singing with a very bad technique, they wouldn't be able to tour at all anymore. But they do, and are able to pull off great shows.
2: I couldn't agree more.
3: Our view on what's technically good/healthy differs. I don't judge any singer's technique before they say they have a problem or it becomes too obvious they have by failing to pull off a show or so. I never said the singers I mentioned are my absolute favorites, just that I like them and don't judge their technique. Here's a list of a few of my fav. singers: Stevie Wonder, Bono, Don Henley, Lara Fabian, Mariah Carey (yes I think she's an amazing singer), Ella Fitzgerald, Shirley Bassey, Sting, Bryan Adams, James Brown, Marvin Gaye. In addition there's a lot of singers whose voices I like but not listen to, like Ronnie James Dio.
4: Again comparing various singers' technique isn't my cup of tea.
5: I suggest you read the case stories in the CVT book before judging it so strongly as you do. Good for you you have your technique under control.

I also have a 3½-4 octave range, pretty much exactly the range of a normal electric guitar. I don't feel more limited than you either in terms of using it. Anymore. Not too bad considering I've had singing lessons (CVT) for only a bit over half a year. I still have stuff to learn, although my teacher wondered if I would continue studying.
6: LOL. The sensations (or lack thereof) in my throat tells me if I'm on the right track or not. I don't try to imitate other singers too much, I won't ever sound exactly like them anyway...