Dear everyone reading this thread:
Please ignore the false information Vince.1551 just spread.
Thanks,
Brain.
I'll provide the correct info to those that don't already know it, since you were to focused on slamming Vince.1551 to do so yourself.
Vince.1551 has it exactly backwards.
What happens when Nikon DX lenses are used on Nikon FX camera bodies is what users need to be aware of.
DX lenses are designed to project an image circle that works with the reduced size of the DX (APS-C) image sensor.
FX is a full size image sensor and while DX lenses can be mounted and used on an FX camera body, a DX lens only illuminates the center DX size portion of the full size FX image sensor.
FX cameras can detect that a DX lens is mounted and they then, as a default setting, FX cameras only use the central part of their bigger image sensor that is the same size as a DX image sensor.
It costs about 4 times more to make the bigger FX image sensor than to make the smaller DX image sensor.
It costs less to make a DX lens than it does to make the same lens an FX lens.
Because the DX lens projects a smaller image circle the glass lens elements can be smaller in a DX lens. The lens body can be smaller too.
Upgrading a lens is usually a quicker way to image quality improvement than upgrading your camera. However, good lenses often cost more than entry-level DSLRs do.
Also, lenses do not need to get upgraded as often as camera bodies, from both a performance and a marketing perspective.
In other words camera body upgrades are more about features and functions than they are about upgrading image quality.