The pixels are bigger & take in light at a faster rate.
personal disclaimer; that's what I read once. I'm not scientifically qualified to say beyond that. and what is "effect." Also, that suggests a theory, if it is even true, to explain dx to fx, but not why, if this is true at all, the 700 owners seem to have more unabashed praise for their d700 camera. There could be a secret gas released as the box opens but goodness gracious is it ever a nice camera, for indoors & nighttime.