Your statement is correct, but not relevant. Even if they had total market dominance, it would be a stretch to compare them to somebody using physical violence, and they certainly don't go out of their way to lock you into using gmail (compared to Yahoo, for instance, who didn't let me set up email forwarding without upgrading to a paid account).
Physical violence isn't the only form of might. "Might" is a synonym for power. And ownership, which is what squintychino claims justifies their actions, is certainly a form of power.
