
I'm a huge Attenborough fan, and don't see the need to replace his narration for the American market, but people will probably watch this JUST for the Oprah narration, which will get it a wider exposure, so I suppose that's a good thing for an educational film.
I'll probably wait till Blu-ray to watch this anyway, and that will probably include the Attenborough narration.
The way that they air these things on Discovery you practically have to get it on Blu-ray to see it all, unless you plan to watch all twelve hours in a single week.

(My DVR will only hold about 10 hours of HD programming total)