For me, higher ISO has much higher priority than pixel number. If my nikon D80 has D700's noise performance, I don't mind downgrading mine from 10MP to 5MP. Larger pixel number also suffers from data storage problem. (Maybe it's just me. I store raw files.)
However, all camera manufacturers, especially sony, like to go the mega pixel direction. Maybe it's because it's easier to advertise on mega pixel than noise performance.