[rnprdk]

Ad hominem can be completely appropriate if you're making a point about someone's character/credibility. I don't know why people think that ad hominem means you should never make arguments "to the man."

In this case, I think he's saying that because these are politically motivated shareholders, a reasoned answer would be lost on them. Cook could have whipped out a lengthy powerpoint full of charts and figures, or he could have done the chicken dance, or whatever ... he's saying the shareholders are not asking the question in good faith.

edit - Further, saying what you would prefer Cook do if you had asked the question isn't entirely relevant, since presumably you would be asking sincerely. Cook can probably tell those guys are only there to yank his chain and make him look foolish, so unsurprisingly he was somewhat hostile in response.