It normally doesn't make a huge difference, but I just got the King expansion, which gives major bonuses for those people who build the largest city and the longest road, and this slight difference in scoring may change the outcome of the game.
The situation is similar when it comes to cities that use the same tile twice. In that case though, it seems to me that you wouldn't count the tile twice; the size of the city can be measured as the number of tiles it spans.
However, when it comes to the road, it's not about size, but about length. If you score a point for every tile that you go through, and your road is long enough to circle back to a tile you already scored, do you score it again?
What are the "official" rules about this?