Assalyan...
Seen a lot of irresponsible shooting at waterfowl over the years.
I think the prior response was directing you toward the fact that their is a huge difference between real "skybusting" and responsible shooting over dekes.
I define skybusting as shooting at ducks that are at marginal range or beyond. The ducks could be simply flying by (pass shooting) or flying by the spread for a look,jumping off the water, or in the worst scenario, working some other hunters' spread.
I've seen hunters shoot at ducks repeatedly at 60-70+ yards (geese MUCH farther) with no apparent effect but a couple of cripples. Why they do this, I'm not sure. Boredom sometimes? False hope- ie. they once knocked one down from that distance? Can't control impulses? The common factor seems to be that they lack the hunting skills and knowledge to pull birds closer.

For me with steel shot I would say my responsible range is inside 40 yards (preferably much closer). I kill ducks regularly by pass-shooting and jump-shooting, but mostly I hunt over decoys. I select my shots carefully, and I kill most of the birds I shoot at stone dead. Most of them when they are "locked-up" or at least flying over the spread.

I don't know where you hunt, but in our area even as hard as my partners and I work at it, we would not get much shooting if we waited for the ducks to actually land before flushing and shooting them. We get "educated" ducks to come close enough to kill, but the vast majority will spook before actually setting down. We do not take risky shots. We cripple very few birds and almost never lose one.

I'm not even sure it would be an advantage to shoot ducks jumping off the water. Most shots in that case must be "going away" targets (tougher feathers, less exposed vitals).
What could be a surer kill than "incomers" with their wings spread with head/chest area exposed? Granted, direction makes little difference on a duck you hit with the center of the pellet spread at short range.

To summarize I agree that skybusting=verybad!
But there is certainly nothing wrong with shooting at birds coming in to your spread; generations of waterfowlers can't be all wrong!