DX Lens Question

I understand how FX lenses behave 1.5 times the FL on a DX body. DX lenses (e.g. 35mm 1.8) behave the same way on DX bodies, i.e like a 52.5 mm lens. If that's the case, what's the deal about DX lenses? Is it just the smaller size?
TIA,
Lawrie