Hmm, from a British point of view this is less true. This is due to a couple of factors, namely that British cars are very rarely equipped with cruise control and our road layout is a lot different.
Cruise control is of very little use on the roads here, as unlike in America, our roads are neither straight nor long. There's plenty of bends and junctions and a near constant need to speed up or slow down as a result. This somewhat makes changes of speed inevitable and also reduces significantly both the need to and desire to pass other drivers on the road.
Most drivers choose to wait behind someone travelling under the speed limit (I agree this can be extremely frustrating), simply due to the danger involved in passing on a road that is not guaranteed to remain straight. Where they do pass the other driver, the slower driver is unlikely to be able to try and overtake back for quite a distance until the road permits. By this time it is highly likely that the other driver will have turned on to a different road.
The overtaking system is also different in that very few roads have a dedicated lane for passing slower moving vehicles, requiring you to move out and face oncoming traffic instead. Additionally many of the longer roads are smaller country roads, often consisting of single lanes with passing points, making overtaking a virtual impossibility.
As for dual carriageways and motorways, anyone overtaking and then pulling back in front of you at a slower speed should be dealt with using the weapon known as the horn. Motorways usually have at least 3 and up to 5 lanes, with traffic moving outwards until it reaches the desired speed. When I meet traffic in the outside lane travelling well below the set limit I however can certainly empathise with your thoughts that these people are morons.
And yes, before someone points it out, I know I shouldn't say British cars, since we make next to none of our own since the collapse of Rover. | 
