The rest of pack adapt much quickier then him, especially Toyota and both Bulls drivers.
That says a lot, given that Coulthard is most famous for not being able to adopt his driving style one iota. 
Having thought a little about Heidfeld's case, I think he should be given another season at BMW. The regulation changes and that the cars will be using slicks could help him to get his qualifying performances into gear. Heidfeld is experienced and makes a good test driver which is important for a team with ambition like BMW. Also, he's maybe not quite as fast, so BMW shouldn't have to worry about driver wars like those seen in McLaren, and it could give Kubica a easier run at the drivers' title - if the car is fast enough next season. With Heidfeld, BMW would be sure to be on for good points race in, race out and if Kubica retired from the race for any reason, Heidfeld would be there to pick up possible race victories. Finally, Heidfeld is German, so that is good from a marketing point of view.
You right with Coulthard but he is already on his way out plus he is quite old so I guess it's double trouble for him to adopt new things.
I'm not denying that NH is still fast, but his qual problems dosen't give him much room for race. Like every driver he had some ups and downs but age is not helping him for sure therefore at some point of his career the downside will take upper hand.
BMW need an experienced driver but then Alonso would do anyway

Given that he is agresive driver as well he should be able to challenge a few guys over there.
As for the staff with nationality, I never really belived that this would be a major fact for any team. At the end of the day would you prefer challenging driver from etiopia or average from your country as a team boss? Plus there is few more german in the pack.
Still it's all theory as we don't know (at least I don't) what is going to be with next year car, perhaps it will suit him better.
Don't get me wrong. I have nothing against him but I don't quite belive that he is going to be at the front anymore. Middle pack - yes, of course