An interesting observation Ultralights.
Many years ago I regularly attended flyins and airshows. One thing I noted was the very poor attendance of fly-in aircraft on the days when the weather was poor. This suggests to me that the majority of VFR pilots (I include ultralight aircraft) dont fly in bad weather. Which, unforetunatly, contradicts the implied claims, that on a poor weather day, every VFR aircraft in the country will be found loittering just below the clouds hopeing to upset IFR pilots.