With more flap you land with a lower nose attitude. With a swept wing aircraft the higher the nose attitude the closer the wingtip is to the ground for the same angle of bank.
That may be generally true with early fighters such as the Mirage and F100 Super Sabre that had marked high nose attitudes on final and touch down. I am not sure about the 737 though. It is interesting to note with the 737 Classics that the final approach body attitude for an all flaps up landing is only one to two degrees higher than a flaps 30 approach. (Ref FCTM). In other words around 4.2 degrees nose high with all flaps up. So in reality, the difference in ground wing-tip clearance between all flaps up and flaps 30 is insignificant in the 737 Classic at least. I don't have ground to wing-tip clearance figures to hand, so I may well be in error on that last statement.