In all seriousness it's a bit of an odd one though isn't it. After all they do sell products to keep your leathers in good Nic and that's polish or wax or Summat similar. Never had a problem on any bike seat I've had but my leathers are 3 years old now. Don't think I ever did though
This is clearly a question for a tribologist
Firstly we must consider the relationship between force (N) and weight (W) which in a static body are essentially the same and acting in opposite directions.
Similarly, at the point of impending motion the applied force (P) is equal to the opposing (frictional) lateral force (F).
A heavier object (greater W = correspondingly greater N) will, quite obviously, take a greater amount of force (P) to overcome the opposing frictional force (F) acting against it.
Therefore, the greater the weight of the object, the greater to effort required to overcome the static friction. (irrespective of the type of material although the difference in coefficient of friction of leather and deregeur urban cammo should really be considered at this point)
Bay says he has never had an issue with leather ... i.e. when wearing leather he does not "slip"
So gentlemen ...
At this point we could consider kenetic friction but let's pause there, review the facts and draw a conclusion.
Bay is a fat ****** so doesn't slip.