Planet Earth (David Attenborough's latest) was clearly made for the export/commercial market. Firstly there were the dreaded recaps at regular interval clearly marking the potential advert breaks and secondly there was a ten minute extra filler on making the programme which I image would be dropped to allow for adverts and keep to an hour long episode. This means that what the BBC advertised as an hour long documentary was in essence no more than 40 minutes of new marerial
You're quite right in that the new Planet Earth series has places for ads to go. As for the 'filler' of the making-of part of the show, I think these can actually be an interesting part of the show in their own right. But yes, this allows space for replacement by ads for commercial broadcasters which buy the show for broadcast in their own country should they so wish, to keep it at 1hr long.
It's a sad fact that the BBC can't afford to make these very expensive shows completely under their own steam. They are either a co-production with other broadcasters who pay some of the production costs (you'll see their names in the credits at the end) or the programme has been made very much with the intention of selling to other broadcasters at a later date.
What is quite heartening though, is that Attenborough still has a lot of input into the show, it's still 'his show', and if you watch the making-of part of the show you'll see that the on-location producers (and often crew) are British (ie BBC). In other words, the show is still effectively made for a BBC home audience, as Attenborough's shows always have been. Infact, it wouldn't surprise me if Anglophone broadcasters (Australia, NZ, USA, Canada etc) kept Attenborough's voice-over on the soundtrack, since he is so well-known around the world.
Infact, much as Obama often seemed to dislike the 'British Establishment', he made sure he had a personal audience with Attenborough before he left office, some time last year.