I believe the idea was that those with little SP may not know enough about the platform and therefore "mistakes" could have been made in their voting. Those over a certain threshold clearly would have either had to have invested their own money or been here awhile - and may be more knowledgeable. I think this goal was to give leniency to understand some users who perhaps are new etc may have fit the criteria just due to ignorance of what they were doing. 

Just my opinion.