The weight thing is too simple.

Take the time one of these days and see just how far you can cast some of our 'weighted' flies.

Traditional weighted Clousers can easily be cast 'fishing distances', with a light spinning rod. Some of those that are really 'heavy' I can cast with baitcasting tackle.

Many stomefly nymphs are also easily cast far enough to catch fish with spinning gear.

I can cast a #8 tungsten bead head wolly bugger over 30 feet with an ultra light spinning rod.

Two weighted nymphs with a couple of small 'fly fishing' size split shot and an indicator are easily castable with spinning gear (many every day 'bait chuckers' fish lighter rigs for bluegills).

With an ultra light spinning rod I can cast a #16 weighted GRHE far enough to catch fish in a small stream.

All flies are lures, not all lures are flies. The difference is ONLY in the mind of the individual fisherman.

Good Luck!

Buddy