I agree with Darrell 100%. I came to the same realization that you did after I started shooting on my D800. When I first started shooting DX, a while back, I thought it actually added reach...like having a 450mm lens instead of a 300mm. On the D800 you can see that there is only a perceived reach in DX because the image fills up the DX camera VF. In fact...as many others have said before...it is the same 'sized' image in DX body as cropping the center out of an FX...just like the D800 shows in the VF. I now shoot all FX on the D800 except when I use my only Nikon DX lens (10-24)...that will be ugraded eventually.
Dan (Nikon D800,V2,Sony HX400V,Lumix ZS40) "I don't read, I just look at pictures" - Andy Warhol