Keep in mind HP is not everything. As some are sadly misled to think. A druid has a heck of a lot of health because they need a heck of a lot of health. A paladin could use more health, but their skills and talents generally compensate.
As a healer I personally prefer healing the lower hp, higher avoidance tanks. The high HP tanks seem to be just mana sinks. But everyone has their own preference.
Let me find that quote from the Lich King tanking guide posted here...
Quote:
Since Paladins are the only tank in the game that can reliably be Blocked Capped nearly 100% of the time thanks to Holy Shield -- reaching the block cap means we have the highest effective health of any tank in the game.
Reference: http://wow.allakhazam.com/db/class.html?wclass=2;mid=1229110515202736947;num=52;page=1
So in essence we don't need as much health because we don't lose it as quickly as other tanking classes.
Again there are always exception...