I've been unclear, I'm afraid -- we ponies are quite familiar with clothing, as fashion statements. Style and fashion are critical in Canterlot especially, but in all of Equestria.

But it is optional, as I myself demonstrate at the moment. [Her shoes and accouterments of royalty don't count as clothing. And frankly Celestia is sick of dressing up.] But it does not appear to be that way for humans, which is what I was wondering.