But why aren't they in sync? What source of energy is keeping that stuff flowing after 3.5 billion years? Why hasn't the drag against the mantle bled off all currents which weren't in sync?
I dunno about all this, I mean I'm imagining the inner earth to be pretty much molten below the crust, at least until we get to the core where the pressue is so great that the concept of liquid is kinda redundant. There's surely more liquid within the earth than on it.

If not charge, but gravity, then the effects are just too weak to account for the lack of energy dissipation. Tidal effects from the moon are significant to ocean currents, but can't account for the numbers involved. (Sorry. A bit hand-wavey, there.)
I'm still leaning tidal. I mean when you think about it, the Earth's magnetic field isn't strong, relatively to other forces we're subject to. Even gravity utterly dominates natural magnetism on Earth. So perhaps it's simply the result of a very large amount of molten iron moving very slowly in fluctuation with, predominatly, the moon. That slow motion is why it's a weak field. The continued motion... gravity is a beast because it's relentless and unyielding. It might be weak, but it always wins. I'm thinking that it's keeping things moving at a very slow rate, the same rate as the drifting of the poles, and that very slow motion is enough to give us a weak magnetic field.

Still want that nobel prize, hand wave all you like!