Gurtogg Bloodboil is pretty much exactly as you describe, the tanks get debuffs that can't stack too high or they get gibbed, so 3 tanks are constantly battling for aggro, when a tank gets so many stacks he'll stop generating aggro and the next tank in line should do everything he can to surpass his aggro maybe even with the help of Misdirects. The first tank has to wait a certain amount of time before he can take aggro (his debuffs will wear off). It's recommended to have three tanks because two really stretches the number of debuff stacks each has to take and is very unforgiving if one tank can't generate enough threat also, and with three, if a tank gets gibbed, it's not a wipe yet. Fortunately there's some frontal AoE in the form of a nature damage breath as well as a cleave to keep your rage up.

On a fight like this, Bears are really great for their innate high TPS and their biggest avoidance stat, dodge, keeps the debuffs from stacking too fast. Really good prot warriors can generate quite a bit of TPS even when not being directly hit but prot pallies really have a hard job because their mana regen really hurts their ability to off-tank and keep up with threat. Avoidance helps keep the debuffs from stacking too fast but he hits like a Mack truck anyway, so mitigation and HP can't be skimped. On top of that, in their top defensive gear, they have to generate thoroughly rude TPS because he also happens to knockback tanks, dropping their threat in an unquantifiable way (threat meters don't accurately reflect the amount of threat the knockback drops).

But this fight is really stressful for almost everyone. Healers are going 100% balls to the wall from about 10 seconds into the fight until he's dead, 3/5 groups of the raid are dancing, and everyone has the ominous threat of potentially being the next to take Gurtogg's aggro for about 30 seconds with the whole raid spamming heals as hard as they can and them doing everything they can to mitigate that damage and keep themselves alive (mages love this fight, heh).