your comments on the US seem to be a question of being used to it. In the US you do not make changes to allow for merging cars/cars behind you. And frankly, in the UK, I thought it was ridiculous people would try and do that. instead, you leave enough following distance to allow cars that are entering/changing lanes/what ever, to be able to do it smoothly without you making a change.
This way every driver sees a much more static situation. It also allows for everyone to go faster. My experience in the UK was that people left very little distance because most of the roads were too shitty to allow for much speed (well, too shitty well outside of London and half decent roads around London were either poorly designed (multiple close intersections on a major artery, including 2 only for pedestrians rather than using a raised walkway) or too naturally crowded to matter.
Of course, it doesn't work that way when you get to some cities like Atlanta and in some areas where people hold the left late even when going quite slow (Florida, where I grew up). But then, I've been in the UK and France and stuck in exactly the same situation. The best at times has been Japan, though speed limits here are super low, so everyone goes much faster than legal and every once in a while you get a stupid ticket because you were unlucky.