Not to hate, but from all I read, it seems people want ISO capabilities far beyond their wildest dream. How much high ISO ability does a person really need? How perfect do one's pixels really need to be? What ought a person to expect out of one's camera? Honestly, a tripod, a broader aperture, and a little patience can make up for a whole lot of ISO...Remember those who want video (or just the movie lighting tools for stylistic reasons)?
To get decent shutter times&apertures - both are degrees of freedom that have artistic purpose, so they can't be changed for technical reasons, as a wider aperture won't give you sufficient DOF and a tripod won't stop motion - ISO 3200-6400 is really nice to have if you have to work within the confines of household electricity.
Now, to get that sensitivity without a nasty hit on image quality a few stops margin are prudent.