Re: BBC documentaries Or Channel 4's Grand Designs
Documentaries (and some other shows) on commercial TV are considerably worse than the BBC equivalent as they lead up to every ad break with "coming up after the break" and follow every ad break with a recap. Consider how short the gaps between ads are getting on some channels then take out the recap and preview section of each segment and then take out the ads and the opening and closing titles and work out how much content there is in an hour of commercial TV documentary.
The beeb make a lot of their programmes forty-odd minutes long in order that they can be sold uncut to foreign broadcasters. However it still doesn't work very well, watch old BBC shows on channels like Dave or ITV 3 and the cuts to ad breaks seem abrupt and somewhat arbitrarily placed.