Shaman are just plain uber-versatile...self-res, heals without losing their high-armor with shields, support for any class, their own high-dps with shocks, chain lightning, and ohdeargodyes Heroism/Bloodlust for insane burst

Some perks you left off of druid though: Boomkins can tank alot better if they pull aggro and actually survive to keep dpsing most of the time; innervate + pala tank = very happy pala tank, or innervate + healer = yay survival; FOREST OF DEATH and/or Your Own Personal Army :P