If someone is going 69 mph in one lane and you're in a car with a bigger engine, you make up ground because you're acclerating quicker. So you normally switched lanes, this may mean going 71 mph. Unless you want to break sudden and cause panic. I was taught it's all about the 'smooth' drive and keeping a common pace.
I think your opinion of the motorways in this country is outdated FIF. Come 4pm on the m1, the first two lanes are normally lorries. There's such a variety of ages, types of car, engine capacity on the motorways that there's unwritten rules wrote. As long as it's done in a safe and senisble manner, everyone's fine with it. It's relatively difficult at busy times to get over 80 mph on the motorway.