I'd say it's because it's an Nvidia =p... I think those scores were reached with an ati x800xt with an overclocked pentium.. on avg I'd bet people get around 12k-14k...
actually the highest score 17000 is by a x800xt as well as a 4200 mhz p4 ee (uber ocin) http://www.futuremark.com/community/halloffame/
there arent too many amd's on the list because amds arent oc'd as high i counted 5 amds none which passed the 15000 mark