Who needs tanks?

Generally when I get a random heroic with slow waves, such as Culling of Stratholme or Violet Hold, I throw on my dps gear because I know I won't be taking much damage. Yesterday my Violet Hold pug got extreme. Everyone had ICC 10/25 gear, so dragons were dying so quickly I hardly took any damage even in my cat gear. I suggested that the priest go shadow since I didn't seem to need heals, but he only had 2 healing sets (like many priests I know). I had a brilliant idea - if he can't dps, then I will. So I switched to my kitty spec and proceeded to 'tank' the rest of the trash in cat form. I managed to keep threat over the shaman most of the time, and between a great healer and frequent cooldowns, I stayed alive. I was cautious enough to switch to bear form on bosses, but I probably could have kitty-tanked them too...

I used to think that healers were irrelevant to (old) heroics, because I take so little damage that it'd be better to have a fourth dps. But now I'm thinking it's tanks who're becoming obsolete. I'd like to do a comparison between 4dps+healer and 4dps+tank to see which group could get through a heroic faster... but where would I find anyone foolish enough to participate?