All flies are lures. I don't know why people try to separate these two concepts. Perhaps it's because one might be carved from a block of hardwood brandishing multiple barbed trebles dangling from every orifice on swiveling split rings and screw eyes whereby the other might be a wispy dun lighting on a spring creek. All flies are lures, but not all lures are flies.
The first and last sentences above are the key to the riddle. I accept that flies ARE lures. In many classic texts on the sport, they were referred to as lures, not flies.
When I look at a tube fly I see a lure that is a fly. It's nothing new, in fact tube flies have been in use for a long long time in the AS rivers of the north atlantic. Because the same materials are tied on a cylinder instead of a hook shaft, nothing changes in the way I (personally, and this is totally subjective) see it.
When I see a wiggle-wart, Vibrax #4, hot shot, Leo's jig, corky n' yarn, hammered spoon, pink worm, etc - I also see a lure... but not a fly.
BTW - When I see a tube fly with a treble hook hanging off the back that sets off my not-a-fly alarm everytime. }>
I guess it's all subjective, like purism. We know our own limits and although these limits make for interesting conversation they are to each his/her own within the bounds of the laws and regulations of the fishery.