>Not trying to be argumentative - just want to be clear on the >facts.
Well in that case, I assumed your OP was supposed to be the 18-55 for I only know of one 17-55 and that is the f/2.8 Nikkor which I would hardly call cheap or define as a kit lens.
But still, the 18-55 that's listed in your profile slower variable aperture and seems to be working fine at wide angle, and the newer faster lenses would by design have a narrower DOF when shooting wide open aren't; perhaps there is a slight variation there. But again I know you are diligent in your testing and I'm sure you took that into account.
But again I don't feel this has anything to do with DX versus FX designs, and is more due to calibration tolerances and luck of the draw.