Ratings for films in cinemas - how they vary across the globe

Throughout the world, different countries censor films with different age ratings, from using the IMDB website again I can see what films that would be considered to cause little offence would cause greater offence in other countries. This is mainly based on the DVD releases, some can be the actual cinema ratings.

Here are a list of Films and the rating in the UK, then any countries with a surprising change in rating:

Titanic’s UK rating was 12 in South Korea it was considered an 18, even more closer cultural countries to the UK like Norway had its rating at 15:
http://www.imdb.com/title/tt0120338/

Also with Batman begins with an age rating of 12A verging on PG, but again Norway opted to censor it at 15:
http://www.imdb.com/title/tt0372784/

But there are cases where the UK seem to over rate films or so it would appear, Christian Bale starred in American Psycho in 2000 and the UK censorship board gave it a rating of 18, where as Denmark and Japan opted for a 15 rating:
http://www.imdb.com/title/tt0144084/

You could argue that in particular countries try to limit the number of people who try to watch a film as it may have a negative or derogatory reflection of a particular country, its also a case of politics, some countries try to keep its population in its own ideologies and representations such as communist countries like South Korea, China and particular former Soviet states.