The center is a moving target :-) And I think the right of the SPD, just like the left of the CDU/CSU as it befits a Volkspartei [how do you say that in English?], are beyond the overall centre.
I think major party is used for Volkspartei. It is true of course, that the parties are overlapping. And people like Bluem/Geissler or Clement/Schroeder could be in the other party if only economic policies would count (Bluem/Geissler could even be in the left party then).

You yourself contended that Merkel's current leftist economic policies (and perhaps foreign policy, too) run opposite to her and the CDU's 2005 campaign platform. (I could say her lust for power was so strong that she broke all her election promises to get into government in a Grand Coalition ;-) ) The media love for her dates from before the elections, and in fact, I even read some 'reformist' criticisms of her.
She has broken most of her election promises, except the VAT increase, which was probably among the most important ones. But it is very clear, that the 2005 campaign platform was far away from the center of people's opinion. And of course there are people critisising Merkel for breaking her promises, e.g. Friedrich Merz and co.

RTL, Sat1 and Pro7
Thought we speak about serious journalism. Last time I viewed news on one of these channels, I couldn't detect that. I don't think these channels make people more conservative. I think these channels make people more unpolitical at all, which as it is 'Unterschichtenfernsehen' admittedly helps the right.

Der Amerikaner ist die Orchidee unter den Menschen
Volker Pispers