So in short, as a German I was puzzled by his "Das ist auch gut so" remark.

What do I care about his private life? His sexual orientation is neither an advantage or disadvantage.
Either he is competent or not.

Trying to market his sexual orientation as a political advantage did insult me a bit. Why in the world would his being gay make him a superior mayor of Berlin?
"Das ist auch gut so"
Being a former POW doesn´t make McCain the best Presidential candidate. Likewise being gay - on its own - didn´t make Wowereit the best candidate for mayor in Berlin.