I'm sure you may already know all this but, basically In Northern Ireland there is a divide between two religious communities. One believes that it should be called just Derry the other believes it should be called Londonderry. So if it was only called one of the two options then the other group would well.... not be very happy! Which you may already have seen from the flag debate over here, the tension between the two can not be the best at some times! So the media report it as both to keep politically correct. I've tried to write this as politically neutral as possible without offending anyone. I hope this clears the whole Derry/Londonderry thing.