Flying into CLT today, we heard Northwest go around twice. They came on the radio and said "approach, the reason we went around was because we are not allowed to land when crosswinds are in excess of 15kts below 1,000." Finally, they took the right side (36R) and I assume got the landing in. This was from a DC-9. Winds were gusting today...310@17G27 at one point. Anyone know what this rule is all about?