Yeah @srean gives the example of the different areas of strips at different lattitude, that's a good one - and I think if you imagine wrapping the unit square (2 values randomly between 0 and 1) to a sphere in a lat-long way, the whole top and bottom edges of the square get contracted to single points at the top and bottom latitude locations (respectively) on the sphere.. so if the point density was uniform going into that then it surely won't be afterwards ;)