> Who cares about controlling the problem?

Well, if procrastination is liable to hinder you in buckling down to learn things, it's pretty important to find a way to really control it. Otherwise HN/the internet will be just be replaced by some other distraction offline.

How likely is it that your procrastination is really limited to whatever manifestations it currently has on the internet, rather than being a general problem you have to correct?

If it really is limited to certain sites, then getting offline or blocking those sites is a reasonable productivity hack, but otherwise you're just sidestepping the real issue and it'll only come back to bite you in other ways later, no matter how many times you change your environment.