Overall, I think both you and ThatBritGuy are right in part: SPIEGEL is fighting off sensed rivals here, but the German blogosphere is so undeveloped that no part of it caught me so far.

Most are unpolitical, self-opinated, self-centered, and unprofessional.

With the "most" qualifier, this is true for the US Blogosphere, too. And at least the middle two is true for somewthing like 95% of blogs. (I say so and I am DoDo!)

Whatever one writes about blogger, afterwards they'll beat you up, because one has understood nothing or spoken with the wrong people. Its a bit like nearing a sect, which is in permanent internal battle.

LOL! Hey Mr. journalist, welcome to the Blogosphere! That's how it works! In the US, too! The Blogosphere is in permanent turmoil, like a quarreling sect, or even more like multiple sects (which is not a positive trait of it, I note). All this tells to me that the author is 'in awe' of American bloggers (and, it seems, more the [far-]right-wing bloggers - quoting Glenn Reynolds) without reading them. Some other evidence of his cluelessness:

Blogs are a niche.

As they are in the US. (Very often, blogs boil down to preaching to the converted - still, that can result in power, if large numbers collect in one 'sect' and are ispired to act together.)

"In Germany the lust for argument is underdeveloped."

This may be true in general, and may fit the situation and views of the quoted German blogger, however: in the US, too, political blogging started out primarily as a thing of 'extremists' (scare quotes because opposing the Iraq war was apparently extremist on one side, while "we should seize their oil, kill anybody who resists and convert the rest to Christianity" is something for primetime on the other side); as the outlet for the loudest voices. Still, Detlef et al has a point that in Germany, people with off-center views can usually have a party, so less need for an outlet - but there are examples, like the infamous Davids Medienkritik (an English-language German blog ran by a Likudnik extremist).

Political blogs in Germany are practically non-existent. When US-Journalist Sean Sinico during the election battle 2005 researched in the German blogosphere

It's one thing that the German political blogosphere is underdeveloped, but quoting something from 2005!? This journalist doesn't appear to have any sense of how rapid developments are. Say Daily Kos exists only since 2002!

a forum for disappointed social democrats. Day after day ranting about the short-comings of neoliberalism, about reforms which are allegdly all false - as surprising as the political editorial of the FAZ

A development along the same tracks the US blogosphere followed.

_{*Lunatic*, n.
One whose delusions are out of fashion.}