Yeah my PBS station did something similar in that my first story was Robot and my second one was The Invasion Of Time, the beginning and the end of Time-Life's original package. But people are turing off the show bacause in their eyes it's too complicated, the webisodes aren't helping matters either.
Are they really turning off?
Comparing roughly the first week of 2012 to 2011 for viewing figures.
In 2011 the final figure was 7 069 000 (which would have been for the return after the mid-season break)
In 2012 the overnight figure (for the season premiere) was 6.4m. By the time the final figures come in it should be around a similar mark as to last year. In terms of overnight premiere (this season to last) figures I think the difference is only 100 000. Of course last year it did't have the Para-olympics to compete against.
Once you exclude reality TV such as the X-Factor, the soaps, and sporting events. DW would more often or not occupy the number 1 slot. As it is it's about the most watched scripted Drama show in the UK.
If you look at the yearly charts,
2010, The Christmas Day special comes in at numer 10 (beaten by Sports/reality and soaps) 12.1m viewers
2009 Christmas Day Special comes in at number 7 (11.57m) beaten by sports/soaps/reality and a comedy.
2008 Christmas Day pecial comes in at number 5 (13.1m) once again only beaten by sports/reality/soaps and Wallace and Gromit.
2007 Christmas Day Special (13.31m) comes in at number 2 beaten by a soap.
So the viewing figures in general do vary somewhat for DW, even during the normal season (usally in the 7-8m for the final figures)
So there is little evidence to support a massive drop off of viewing figures for the BBC to be concerned about.