Increases chance to hit by 5% is pretty much accuracy. Also it's a stance unlike internal release which is a buff. It matters more to see increased stats in a stance than a 15-30 second buff with a cooldown. The reason why I think the extra accuracy from the stances should be added to the accuracy stat is so that tanks can optimize gear easily. It's not to hard to use a calculator but it really shouldn't be necessary because the stat increase should be visible. There's no reason for it not to be, bug or not.