I don't think St. Helena has many wet runway days per the official description but prudent dispatchers usually use wet runway lengths unless that becomes a problem and the forecasts are favorable. That brings up another point. These current 737-X and small A 3XX's are "lead sleds" on the runway at higher weights. The 737 started out 50 years ago as a 110K lb aircraft and is now up to over 187K lbs. The wing has been increased but only by about 20% in area. Most of the weight increase has been accommodated by much bigger engines and brakes and much higher runway speeds. The B-757-200 is not a led sled and has runway speeds typically more than 10 knots less than the smaller aircraft. The runway speeds of these small aircraft are greater than the original turbojets. It is also generally true that larger aircraft with larger spans are less affected by turbulence. I think it all started going wrong when they put brakes on the aeroplanes and got rid of the tail skid and grass runways.