This 'variation' is almost certainly a manufacturing defect.
The die that made this figure would have a spindle near the foot the plastic would form around, creating the foot peg. When I was making auto parts, this spindle was called a 'core'. Not sure if the same terminology is used in toy manufacturing.
Anyway, those spindles are subjected to a lot of heating and cooling, and being so thin and long, are prone to breaking off regularly. When one breaks off, the hole can no longer be made, and you have a 'filled in' foot peg. It's probably a minor enough defect that Kenner would not trash those made with it, but would simply replace the broken part and continue.
I hope that explains it. If anyone has an alternate suggestion, I'd love to hear it.
Ian