Older 1/1.6 cropped cameras had narrow viewfinders because they were adapted versions of 35mm film SLR's and the viewfinders were still set up for 24x36mm but masked off. More recent DSLR's including the D80/D200/D300 fix this problem. However, the cameras still use the same lens mount as the old 35mm film cameras, which in particular means the lenses are made for the same (larger) clearances between the mount and imaging plane as for the old cameras. That means to get the same angle of view as a full frame 50mm "normal" lens, you have to go to a 30mm or so focal length, apparently requiring a wideangle design even if you're covering just the smaller 1.6 sensor area. The flange-to-sensor distance was designed for 24x36mm and is mismatched to the smaller sensor, which puts some cramps into the possible lens choices. This wouldn't apply to (for example) the Olympus 4/3 system, where the whole mount has been designed from scratch so they can bring the lenses closer to the sensor.
The full frame sensors also have the advantage of simply being bigger, so they can collect more total photons from the same exposure at the same f/number. That's why the 5D and D3 perform better at high ISO than small sensor cameras. This article explains the effect:
http://www.clarkvision.com/imagedetail/does.pixel.size.matter/