I agree with sparhawkes statement as well but there are also many other variables. Some names have Age, Backlinks, PageRank, and many other attributes that would push someone to bid on names that otherwise look worthless. With godaddy you have a combination of bidders ..not just domainers you have marketers, end users, domainers, speculators etc. So truth be known we may never know the reason but I bet a good portion is because of the things listed above.