None of your observations strike true, perhaps you are assuming too much thought on the part of the average user. People use 'Login with FB' (and others) because it is convenient, there is nothing more to it. It's only a small fraction of the population that are aware that choose to avoid using it due to the potential for lockin.
Yeah the remark about businesses was more persuasive. Banks and other large B2C organisations are much more likely to care about commercial lock in and the compliance risks of using Facebook login than consumer users.
