There's nothing in the regulations about starting a move. It's also impossible to write a rule which encompasses every conceivable scenario. And it's fine to believe that Rosberg was in the right or Hamilton was in the wrong. But it's not what this rule says.
Hamilton probably fell afoul of this same rule in Austin. But, it was the first corner of the race, the wet conditions gave plausible deniability, Rosberg wasn't hit, and they're on the same team. Who was going to complain? A crash will always invite closer scrutiny.
Ultimately, the "one move" rule creates as many problems as it solves. Before Schumacher's tactics inspired the ruling, it was the custom not to block. Except in the cases where the guy in front *really* didn't want to give up the position. It's all gray area, despite the attempts to set up binary conditions for decision making. Still:
if any part of the front wing of the car attempting to pass is alongside the rear wheel of the car in front this will be deemed to be a ‘significant portion’