I would like to address this point that Manfred did not. You are not making an apples to apples comparison. It is true that accurate focus is needed to take full advantage of the sensor on the D800. But if one takes the identical picture with a D700 and a D800, with the same glass and exactly the same focus then prints the photos at the same size, the picture produced by the D800 will be a least as sharp (probably sharper) than the one produced by the D700. Having more pixels doesn't make for a worse picture.
John