When they do this, the students find that while the basic language of English that is used all over the world is the same there are subtle differences that separate one from the other. The first point of difference that they notice is that the spellings sometimes tend to be different. Words like colour are spelt differently in the United States and in the United Kingdom. In one style some words are written with s while in the other style it is replaced with a z; organisation and organization is a word that comes to mind immediately.
Then when the students continue reading further, they come across more differences. What is called as a lift in one language is called as an elevator in another. There are many words like this that have substitutes in different forms of English. So once again the students have to keep a track of all this and make sure they are implementing all these differences when they write. And yes, there are differences in punctuation and the way questions are asked as well.
The examining bodies expect students to take language formats seriously because when they do not follow the correct style, they deduct marks for the error.