First off, mitigation and dodge/miss/parry are not the same things.
Mitigation equates to the ability to reduce damage you take, this comes from Armor/Shield block rating/Shield Block value
Avoidance equates to the ability to completely negate incoming damage.
and no there is no avoidance/mitigation cap at 60%. Ciderhelm just reposted a thread from the WoW forums where you can attain 106%+ total avoidance/mitigation from gear and talents alone, thus giving you passive crush immunity (meaning you don't have to hit shield block to be uncrushable).