You would think so, wouldn't you? I've yet to see that be the case, though. Look at Street Fighter.. all of the sprites were what.. 128x128? They couldn't possibly have been drawn at that resolution originally, and yet they had to start from scratch when they upped the game to HD. I wonder if that's what's holding back a Mortal Kombat HD remix? Those were photographs, definitely higher-res than anything we ended up with, and yet there's no sign of a new version.
So I wouldn't hold my breath for high-res textures on a remake. GoW didn't have 'em, either.