A 5 man group of shaman with 5 grounding totems means between 5 and 25 spell immunities. I think they're looking at it and deciding that they really didn't intend to offer so much possibility.

We've seen them do similar things like the debuffs to blessing of protection, ice block and the priest shield. Chaining/stacking immunities is something they've tried to balance against.

Also, it's fairly obvious that stacking shaman is by far the most popular class to stack in a group. Go ahead and tell me this isn't because they are the most powerful.

The other issue here is that the "dispel" mechanism for totems is awkward at best.