I'd imagine that the constant rubbing of a naked screen in and out of your pocket along with constant touching/swiping with dirty fingers will wear down the coating waaaaaay faster than what could possibly happen with a screen protector. It's essentially protected from the elements and the adhesive that holds most screen protecters on your screen isn't usually particularly sticky, it's more of a 'suction' (for lack of a better term) which holds it on.
I'd say the coating will be more than fine under a screen protector.