Stormstrike only does physical damage even thought its charged with energy in the animation.
Then there is the fact you need 2 talents to give it nature damage. One from proccing stormbringer and another from tempest strikes. (proccing any form of lightning)
And when you have windfury on it it just does more physical damage.
While warrior is going to do Stormstrike damage which does physical AND nature. So yea i think the shaman stormstrike is false advertising.