I would honestly prefer a feral druid to OT than a warrior. It just seems like that's what they're designed for. As for utility...yeah you've got the ability for one warrior to provide the extra buffs, but that warrior will not be as useful in 10-mans, where a group could likely have half melee half caster DPS (or mainly casters). My friend's kara guild has either all casters and 1 rogue, or all casters (excepting the 2 tanks). Not to mention a hunter has a buff that will either up the damage of everyone in his group by 3% (which stacks) or which will give everyone in the raid quite a bit of AP. Not to mention a prot warrior can spec
5/5 imp demo shout if he/she wishes.
In melee-heavy groups or in hunter/melee heavy raids, one DPS warrior is good, much like one survival hunter is good. However, if you look at some of the other buffs classes have for melee...
Enhancement shaman have incredible buffs for melee, probably more powerful than imp battle shout.
Pally healer casting BoM?
Hunters providing ALL DPS in their group 3% damage increase (not just melee), or providing a lot of AP for the raid (usually 150-225 AP, depending on gear level).
Feral druids providing 5% extra crit. For those, especially hunters, who have +crit damage talents, that's more than 5% damage increase.
And in caster-heavy groups, warlocks casting CoE/CoS could be much more support than casting CoR on a mob, not to mention the buffs/utility shadow priests, resto/elemental shaman, paladins, balance druids, and magi provide. Even here, BM hunters are able to up the damage of the casters. Warriors dont do anything here.
Now, I'm not saying DPS warriors are inferior or bad. I'm just saying they're not as crazy good as Devioususer is saying. And yes, other classes (rogues don't count, who needs 'em anyway?) are able to provide group/raid buffs.