I read an article about a guide on the San Juan named Andy Kim (I believe he's Korean) who ties the majority of his flies with nothing but thread. Most are #24 or smaller, and a #20 is the largest he ties. He had several, and the article said the secret of the fly was how he manipulated the thread, i.e., flat or tightly wound to segment the fly.
It would seem the definition of the 'fly' would be essentially whatever it takes to represent a likeness of the prevailing food chain item available to the fish at the time. This could be from a tiny nymph or worm, to a bug, to a small fish or frog, large worm or snake, etc.
Yes there are purists, as we all know. But to me, if you're fishing, then it's catching the fish that makes it interesting. If you don't want to catch them, why put a hook on the end of the line. Or, for that matter, why not just tie the fly on a straight strip of wire.
I'm not after the perfect cast. A guide in Colorado told me all that fancy false casting isn't going to catch fish, the fly has to be in the water. Just get it there the best way you can and as much as you can.
Boy, did that ever get off subject...... Sorry guys.