I don't know anything about them, but if the 4 studs that are longer are evenly spaced, then it would make sense that those 4 are for helping pull everything together, and the rest being shorter is so you don't have to spend so much time tightening all the nuts down on longer studs, especially if using hand tools.
Having the studs on the inside also would protect them better than having them stick outside, giving less chance of damaging anything if you're rubbing up against roots and rocks.