You don't, I don't - but conservatives do, media does, the Church does. See the Berliner Morgenpost article I linked downthread -- he was pursued by the media before, and attacked by a bishop and receiving hate mail afterwards (not to mention the East German local politician who spoke about the Nazi death camps). That you are now in the position to not care about von Beust's and Westerwelle's private life (as in: it won't influence their political fortunes) is a result of how Wowereit's coming-out was taken.

Why in the world would his being gay make him a superior mayor of Berlin?

I agree (with the minor difference that I see the marketing kicking off only after they saw the majority positive reaction).

My position may not be clear to you from my top-level comment, so a little more explicit. I would site myself on the hard-left, in German politics somewhere between the Fundi Greens and the Left Party, so "in Schröder's Third Wayist direction" is not exactly an endorsement from me. Media politics and celebrity politics is another thing shared with Schröder (who for example made use of public appearances of his fourth wife in First-Lady style). As for his real political achievements, again, a "not-at-all hard-leftist austerity programme" and making the Left Party bear all the risk for the latter aren't exactly endorsements from my quarter.

That said, I'm still conflicted. There's that I see more significance to Wowi's coming-out than you do, and I believe he has the potential for a better chancellor than Schröder, who, despite his record, might be more progressive (because of being less beholden to some old allegiances than his North/Western German counterparts).

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

You´ve got Brandt, Schroeder, Fischer or Wulff as examples. Trying to use the private life of a politician against him always involves the risk of a back-lash.
That´s why most media won´t use that knowledge.

What do I care about their private life?
Are they competent or not?

Also, consider the case of Ole von Beust. Conservative CDU politician. As far as I can make it out, his father outed him unintentionally in an interview. Just like Wowereit according to your search. :)
And his popularity soared after he fired Schill allegedly trying to blackmail him.

And to say the truth if I didn´t follow the news seriously I doubt that I would know that von Beust or Westerwelle are gay. It´s just not a page 1 story.
Different to Wowereit, I admit. But only because of his "Und das is gut so" comment.