In terms of lore what does this mean and why is it happening? Why does Deathwing (or rather, does he?) have control of elementals?
He doesn't, but he is a pawn of the old gods. The elemental lords were the luitenants of the old gods in the titan/god wars, so the old gods gave deathwing a part of their army.
Join Amicus, 10man progression raiding, but on a respectable 2day schedule!
The Shattering book made it seem like the elementals aren't really being controlled by anything, they are just freaking out due to being sensitive to the upcoming planet eruption that Deathwing is causing.
More this than anything else from what i've read by blues (haven't read Golden's book yet). The lesser elementals are going into hyper drive because of the havoc that Deathwing is creating in Deepholm at the moment. It's causing an imbalance in the world so they're getting unruly.