Think about it. He said something really stupid and indefensible: "Black People Don't Use Macs". (No really, here's Daring Fireball's link to the slide.) As the shit hit the fan, DB turned it up by adding "The only black people at Macworld are outside begging for change." Wow, no chance of any reasoned discussion anymore, not with that kind of communications noise. Of course, it was all just to get people talking how, in DB's opinion, minorities are underrepresented on the Mac. DB had no facts or numbers to cite, according to Gruber, so there's nothing to actually argue about, it's all opinion.
That, by the way, is Dvoraking 101: Say something controversial. Then, when the hubbub starts, say something even more controversial, but have no real facts or empirical data, and make sure it's all really just fairly vague opinion. You see it all the time in the press, especially about the Mac. You want hitcounts? Apply Dvorak 101 to either the Mac or Linux, and BAM! You've got a vertical climb in Google Analytics. It's brilliant, sleazy, and utterly reliable.
But until reading John's article, I had never heard of anyone doing it live. So, it's kind of cool, in a pathetic "Well, I'm -pressed. More de- than im-, but I'm definitely pressed" kind of way.
I imagine for his next session, DB will start with "Women are too busy having babies to be geeks."