It really is not practical or needed on a field gun.
Having guns with and without ribs, and having used them all for clay shooting and hunting, I think that's bull. "Not practical?" Even if you assert that ribs aren't good for anything, do people MISS because they have ribs? That's downright silly.
When you're raising the gun to your shoulder while swinging on a flushing quail, the rib provides a surface with a readily-discernible shape for your peripheral vision. As you raise the gun, the rib goes towards flat. You don't have to pay conscious attention to it like you do with a rifle sight.
That helps you focus on the bird, which is the only way to hit it.
Without the rib, you see something more like a rifle sight, as the top of the receiver approaches the bead in your vision. This can cause just enough distraction to make it harder to make the quick shot. IMO this is exacerbated by a bead on a pedestal, as Remington uses on plain barrels. If it's just a bead on the barrel, I don't think this effect is as severe.
Have I shot fast-moving quail with a plain barrel and a pedestal-mounted bead? Yes.
Have I shot those "Holy crap! How did I hit THAT?!?" birds with one? Not that I can remember. I have with a vent-rib O/U and a SxS, though. Now sure, if I were as good a shot as earlthegoat2, I could probably have done the same thing with a 9 lb. 10 Gauge ribless single shot. Personally, though, I found it easier to do with a quick, ribbed gun.
Bottom line? The vent rib and the two barrels of a SxS both help to draw your mental focus out towards the bird. This is caused by perspective and the effect of a "vanishing point." A bead on the end of a round barrel naturally draws your focus towards the bead itself.
It's not the
easy shots, pre-mounted shots, or predictable, slow birds where you can tell the difference.
(Aside... I have shot doves and 5-stand in desert heat, with a really hot barrel, and I never had any heat mirage issues with a single barrel with no rib. Only a SxS has given me any real trouble with heat mirage. I'm not saying it doesn't exist on a single barrel or stack barrel gun, just that heat mirage alone can't explain why a vent rib is the standard, and has been for a long time now.)