I'll tell you why. his different branded VGA might be overclocked, his PC might be more optimized than yours, and the drivers may be different, every single driver release for the GTX GPU's change the way your scores on things like 3DMark score.
if you want better scores. get this.
eVGA Precision EVGA | EVGA Precision | EVGA Precision
This is by far the best program to Monitor, and overclock a graphics card I've ever used, but be careful when doing it.
This program I have set to run automatically with my PC. it sets the fan speed from 40% to 55% everytime I turn on the PC, it also monitors the temps of the graphics card. and even better. you can overclock it and get a solid 1000 or more point increase in things like 3DMark06 and Vantage.
I always say this. Say you have the eVGA GTX 285
go to a site like newegg.com and look it up. and then use the eVGA Precision program to overclock your card to some of the Pre overclocked cards your specific brand sells. like the GTX 285 SC edition and SSC. and even the FTW. you could probably set it for something in the middle of SSC, and FTW. and go with like 700 Mhz On the Core. and so on.. make sense. check out the speeds of these ones core clocks and memory Newegg.com - eVGA GTX 285