A great fly fisherman/tyer named Tom Nixon didn't see much of a distinction. Look up the thread "Tom Nixon Patterns" and his book is cited as well as a couple of web locations to see his flies. For instance: http://laflyfish.com/flies/tom-nixon-spinner.php. I think Czech nymphing ended the distinction between fly and lure. Since you don't have to cast a Czech nymph, that prerequisite is gone. Since some Czech nymphs are a bit of lead dressed up or a jig equivalent, they can be cast with a small spinning reel. A fly is a lure and some lures are flies.