Wow. Well... Wow. Domain registrars are things you touch once every few years, and their entire goal is to make it more time consuming to remove yourself from them then switch since its such an insignificant task, most people ignore it and keep with the same one.
If vendor lock strategies (which this plain and simply is) were illegal, we wouldn't have some certain monopolies - I doubt, for example, that Windows would still hold such a big market share.
Is this even legal?