+ Dealing with stacks no other tanks have to consider.
A Warrior that only uses Fell Cleave for the 1337 numbers is no Warrior at all. A Warrior still thinks about mitigation and timing when it comes to tank busters, which Inner Beast will take the 5 stacks and put them to better use. Hell, even the job quests for it show the "struggle" for Warriors. Do I let the Beast out of control (and cause a wipe in exchange for that extra hit)? Do I reign it in (and spare the healer kiting the boss around while trying to get my dumb self back up)?
Anyone who is seriously complaining about this are just dps turned tanks who think that damage is the end all, beat all. Not acting like a Tank when you que as a Tank, is a serious flaw.