I'll agree that some 'pruning' could be done but it's still handy to have some little-used categories kept separate. For example, I know very little about TV and films but I'm quite knowledgeable about some aspects of radio, so I tend to ignore the main 'Media & TV' heading and look only at the 'Radio' section. If radio questions get posted within the main category, they quickly get pushed down the list and people like me might not see them.
Chris
PS (For anyone who's unaware of it):
All of the sub-categories can be seen by clicking on the word 'Topics'