Mists of Pandaria introduced Way of the Monk with the monk class in an attempt to balance the several different types of weapons monks can use, particularly given the potential for both Brewmasters and Windwalkers to use either a two-handed weapon or dual wield. The ability did not change throughout the expansion.
Warlords of Draenor
A hotfix during Patch 6.0.3b modified the balance between the two styles. While the result was that Windwalker monks continued to be able to dual wield or use a two-handed weapon by personal preference, the additional attack speed significantly benefited Brewmasters and made the use of staves and polearms the preferred style for tanks.
Hotfix (2015-01-05):Way of the Monk now increases the Monk's autoattack damage with one-handed weapons by 25% (down from 40%), and increases the attack speed of two-handed weapons by 55% (up from 40%).