Upload & Sell: Off
You are absolutely right Ray that a DX sensor will often hide the weaknesses of a lens at the edges. That generally is not of much concern for me since shooting wide open the edges tend to be blurred. I don't need them to be sharp. Also, if there is a touch of vignetting that isn't a problem for me either. My comment was certainly not that the lenses are "better on full frame," but rather that shooting at the native focal length makes using them easier on an FX camera. Doubtless, the talented folks using these lenses on DX cameras are capable of accommodating the cropping factor and the resulting extra length. Yet, I recall feeling almost a sense of relief when I mounted the 17-40L on the 5D and suddenly had a real wide angle lens. Yes, it had been very useful as a walk around lens on the 20D at about 28-64, but I loved having it at its native focal range. Then my 28-70L could do the job for which it was intended.
Better or worse? Not at all in my lexicon. Familiar and comfortable? That's it.
The only thing I'll add here is that some of us who haven't been shooting seriously for as long don't have the same notion of what a given focal length "should" look like, i.e. that the field of view it would give on film or an FX sensor is somehow "native" to that lens. What you're expecting from a given lens is not only a statement about the lens, but also (or even mostly) about your past experiences with some lens/body combination(s). So for me it's not a matter of "accommodating" or being talented - to me, what a 55mm field of view "really" looks like is (presumably) to you what an 85mm field of view "really" looks like. No adjusting necessary if I don't have that other idea in my head...