From Diablo Wiki
To/hit is not a property that exists in Diablo 3. Rather than hits having a chance to hit (or not) Diablo 3 handles this basic game system with damage and damage mitigation. Thus players raise their Armor or Resistances to reduce the damage they take from attacks, and raise their mainstat and critical hit to increase the damage they deal out.
It’s sort of common sense in a way, that a range attack has to be aimed and connect with a moving target so a chance to miss in in the player’s skill, so no need to have it on the ability (some exceptions exist). AOE just doesn’t make good sense to miss because if the enemy is in the area of effect that’s their bad. Skills with big resource costs have that investment in them, so giving them a chance to miss feels lame. Skills that can miss are usually the low/no cost melee attacks, spammable attacks, etc. And no, there is no stat or way to augment/reduce chance to miss.
To/Hit in Diablo 2
In previous Diablo games and in many other ARPGs, to/hit is a stat that determines the chances of a attack landing on a monster or a player. Diablo 2 called this stat "Attack Rating" and it was determined by a combination of numerous factors including Dexterity, character level, monster level, item bonuses, skill bonuses, defense, and more.
The Diablo 3 system seems more "logical" to most fans, since the way that very high armor means not getting hit at all seems silly in some games. In Diablo 2 for instance, a high level character with heavy armor could stand motionless in the midst of a dozen low level enemies and only be hit by 5% of their attacks. A character can do the same in Diablo III and not take enough damage to matter (since high defense = damage mitigation), but at least the low level enemies aren't endlessly swinging at a stationary object and hitting nothing.
- Bashiok explains defense and to/hit - Bashiok, 8th February, 2011