Thank you for saying it. I too am sick of hearing stories like this, from either side. I don't need to know this one's great-grandpa was an immigrant milk man, that one's father went to Harvard, so-and-so's uncle was a mobster.... Let's just let everyone run on his or her own virtues or vices and stop worrying about lineage.
While I understand and agree with your sentiment, the mythical construct of his father is being used by him to emotionally manipulate voters. Pointing out the mythical nature of his construct is proper. Though, in fairness, it probably could have been done in fewer sentences.
Normally, I would agree with you, because that's the American way. People should be judged on their own personal merits, not on those of their forebears.
But in this case, almost all of Obama's political resume is built around who his father was. Therefore, it is as useful to know who his father really was as it was to delve into the real military service of Lurch when he made Vietnam the centerpiece of his campaign.