I think that those of us who have a long history as watchers, but are not knowledgeable about the physiology or training aspects, tend to notice "bad" feet but not really appreciate "good" feet. As I mentioned before, people like me -- and there are many of us -- really benefit from this kind of education.
This is the thing Bart, I think that every dancer developes a peculiar and singular relationship with their feet, throughout the course of their training and into professional life.
I had a full training but in my second to last year it hit me that I didn't want to be a dancer, so I left when my training was over, made up for the education I missed and then went to university.
At the start when you're assessed as a child it is on the arch, as purely an aesthetic construct. It also seems that a good arch comes with some degree of hyperextension in the leg and while these qualities are most definitely prized they begin to throw up problems which you have to find ways to counter that straight-legged un-arched feet don't.
Pulling up on the leg is harder, the construction of the leg and and foot constantly want to throw you off balance, likewise it's harder to turn a great deal of the time, feet are uneven surfaces at the best of times and most damagingly the 3/4 pointe which is essential for ballet starts to put a great deal of pressure on the achilles tendon - leading to that bane of dancers spurs.
When I was 16 I started to get pain in my achilles an x-ray confirmed that I had spurs in my ankle (bone growths at the back of the ankle shaped into sharp points) an over arched foot just going through the motions of a tendu places far greater stress on the back of the leg and ankle, just because of the extremity of movement in an arched foot. Also rising to pointe, 3/4 or full also takes the stress on the lower leg to a greater extreme than the straight pull up.
With spurs there are three options, suffer in silence till it's chronic; find a new way to work the foot - hard as ballet is a technique of extremes or surgery which requires nine months of total post op rest. I stopped altogether eventually, not because of the spurs but it was a factor knowing that it was a chronic condition which would only get worse.
For a layman the beautiful arch of a foot is lovely, it's something beautiful to look at to be sure. The mechanics of technique and how it effects the foot and the stress that places on the whole frame is something dancers live with constantly.