Worth noting, of course, that some part of Tumblr's growth has come precisely from their equivalent of a BlogThis! button - it just took a few more years.
The linked article isn't just saying "Yahoo may change the terms of their deal" (and pray they don't alter it further), which everyone knows they can and almost certainly will. It's saying "I, Dave Winer, will draw from my own personal experience, including my interaction with one of the participants of this deal, to speak with authority on this".
Like bringing up a character witness in a defense trial, such supporting arguments legitimately open up the speaker themselves to critique.
I honestly don't understand the problem with that. He has experience, with this type of situation, and with the people involved, and he's using that to back up the more general point (which you agreed with). Why is he not entitled to some authority here?
It just seems like a lot of the commenters have much more of a grudge against Dave Winer the person (I don't follow him that closely) than the actual content of his argument.
Winer has fielded a number of seemingly bitter and aggrieved posts lately (about ageism, not getting his due rewards, etc) and it is impossible to read newer entries without that cloud however over them..
There is no "you should question this because his name is Foo", rather "you should question this because he is acting Fooish, which incidentally sounds similar to his name."
Immature, but not an ad hominem.
That's backwards: ad hominem attacks are considered bad precisely because they're not relevant to the argument. Note that the GP's argument is exactly the opposite: that the attacks aren't ad hominem because they are material in this case.
If you're saying that the original line wasn't meant as support of their argument and therefore doesn't qualify for examination for materiality, I'm finding that hard to swallow too, e.g. "You're wrong, and also incidentally--totally as aside, seriously--you're an idiot."
If I say "You are a doo-doo head, and you are wrong because of X, Y, and Z", then (assuming X, Y, and Z are sound of course) I have not committed a logical fallacy (though I have immaturely insulted you). The insult was not a part of the argument presented. If I say "You are a doo-doo, and therefore wrong.", then I am guilty of fallacious reasoning.
Things don't have to be fallacies for them to be out of line. We can criticize "You're wrong, and also incidentally--totally as aside, seriously--you're an idiot." without mislabeling it as fallacious.