"Just do it" ads started in 1988, almost a decade before Think Different campaign, here's to compare:

http://www.youtube.com/watch?v=ENi1SvEFqsQ

Thanks for posting the Jobs' ad introduction, I've seen his talk before, but I as watched it after reading both the article and Isaacson's bio I saw something new and different.

I also have an impression that Rob Siltanen didn't remember correctly the Jobs' attire on that day as he saw him, that it was not actually a "black mock turtleneck" but a black sweater just like in the video.