It would be an interesting statistic to see on the list of those who have achieved it. Bodyweight that is.
The other end of the scale interests me too, are there many heavyweights that can manage the pullup with the beast in tow?
I've spent countless hours in gyms helping big guys crack one unweighted pullup over the years, where many of them could lift me with one hand if they had to. I imagine it would quite rare for someone weighing more than 240 lbs to be especially gifted at pullups.
Little guys seem to have an advantage with weighted pullups and bigger guys have the edge on the MP. Knowing the bodyweight of whoever attains it would really put it into perspective.