The hit runes don't affect their chance to HIT, they affect your ability to hit vs. dodge. There's not any rune, skill, or item that affects a hero's base ability to hit that I'm aware of.

Since mages can be dodged, Hit Rating helps against the dodge as I understand it. It would be nice if there were a lvl60 rune that would improve a mage's actual chance to hit coupled with improved magic attack.