Sorry, I didn't fully explain the idiom: "centre lane" refers to the right-most (what in the US would be left-most) "fast" lane - the one closest to the centre of the highway as a whole.
To your point, I think the middle lane of a three-lane road is, ideally, the correct travel lane. Cruising there at the prevailing speed leaves one lane more lightly traveled for entering and exiting, and the other for passing. Predominantly using that lane minimizes lane changes, which are the most dangerous driving moments. You're right, though, that the strategy breaks down as traffic gets heavier, and gets ruined entirely when (as under discussion in this thread) people gum up the supposed "fast lane".
