Sure there is. iPhone or otherwise, I don’t touch the screen when holding my phone.
Might be an issue for people with small hands perhaps. I’m trying to figure out in what circumstances I would be forced to touch my display whilst merely holding my phone but can’t of one, so it must be a size/grip thing, or I’m just holding my phone like a weirdo.
I mean, I suppose you're right. However, that being said, a case is a good idea nonetheless, just as is a screen protector. A good case protects the phone against damage from dropping, just as a good screen protector does the same for the screen.