Your onto something here ... but aren't the arched feet a replacement for not wearing high-heel shoes? We all like long legs, tapering towards the ends, and shoes do this well. When a girl arches her feet, she imitates the effect wearing shoes would have. It's fantastic, of course, but for me, it is simply a relief to see the model does this once she's taken her shoes off.
Frankly, I wish they kept their high-heel shoes on!
Great thread, and a good insight!