I've seen this dozens of times at my gym. I am pretty sure one idiot started it and everybody saw him do this and now they do it too. I guess they don't want their shoulders or traps to hurt from the bar. Some other weird shit I've seen:
1. Attempts at using the hack squat machine for shrugs and shoulder presses (upside down shoudler presses once!)
2. Smith machine vertical rows (I just don't see the point at all)
3. pushups with feet on one bench and hands on another bench
4. putting the weight stack on the lat pull down machine to the max and then doing pull ups
5. cable flies while laying down on a bench
hahahaha!! This is some funny shit right here! I think people come up with this shit to make it seem like they know something no one else does, as if they're some trendsetting guru who has untold secrets on getting even better results than tried-n-true methods.
"Ya see, you get a much better stretch and development by elevating yourself an extra 2 feet off the ground on benches while doing your pushups. Lots of people don't realize this. Plus, you look totally badass and people will think your weightlifting experience is far too advanced for conventional exercises."
I worked out with a guy one time who tried to show me his "secret" way of training traps by using the calf machine. I wanted to slap him around, but he was my friend. I had him do some heavy sets with a barbell and that put a stop to that.