It's not as simple as 13 vs 11. The problem is that of the 11 ranged specs, hunter, mage, and warlock comprise 8 of the 11 ranged specs. So that's 3 classes covering about 80% of the ranged specs. Then of the other specs Boomkin/Elemental both have competing melee specs in the same class so players may want to play that instead. However, if you want to play a monk, paladin, warrior, dk, or demon hunter and want to dps you have 1 option - melee.