Every TV channel has a mandate, a set of values and targets that influence the kind of programming they do. Every TV channel also has a well defined target audience that they wish to capture. How channels deal with subjects is very much a matter of these values and mandates.
For example, BBC 1 is likely to deal differently with a programme on film history than BBC three, as the latter is clearly specifically inclined towards a younger audience. Film history is a subject that can interest people of all ages, but how a programme is designed usually depends on the demographic the programme is targeting.
Channels don't always product their own content, but the kind of content they broadcast depends on their profile. For example, Sky TV is a data provider and does not get into original programming. However, SKY channels will showcase only specific programming.
Sky Atlantic, for example, is a channel that is dedicated to popular American dramas such as Boardwalk Empire and Entourage. A TV documentary about film history is not likely to be shown on Sky Atlantic.
TV programming is a complex and involving subject and can itself become an interesting area to study in the field of media history.