If you will go to Google Image Search and ask for violinist you'll get lots of pics of "proper" hand positions. Then go back and ask for fiddler and look at the difference. I am classically trained and the inside/base of my index knuckle is nearly always glued to the neck--keeps my intonation right and gives me an anchor. The only time I use the "extreme arched left hand" is if I am going to shift into a higher position, do a long slide (like up to the ocatve harmonic), or if the song has a lot of 4th fingerings.

I tend to agree about classicists not sounding like fiddlers--took me about 6-8 years to overcome my classical training and I still do a LOT of things that "fiddlers" don't do--staccato, spitzacatto, bouncing, etc.