Action boosts go up every 3 levels starting at 1, 4, 7, and 10 - where is 13?
Primary Stat enhancements go up every 4 levels starting at 2, 6, and 10 - where is 14?
Spell Damage Amplification (Cleric/Bard Healing or Wiz/Sorc Damage) go up every 3 levels starting at 1, 4, 7, and 10 - where is 13?
Toughness enhancements go up every 3 levels starting at 1, 4, 7, 10 - where is 13?
There are many more examples (Barbarian Damage Reduction, Extra Rage, Hardy Rage, Power Attack, Will Power, Bard Extra Song, Human Improved Recovery, and the list goes on).