A comment on John Nack's blog post Why your Web content will look darker on Snow Leopard explains the origin of the old Mac gamma. While the gamma change is hardly news to After Effects users, there's more in the post, like a quote by Adobe Principal Scientist Lars Borg, "the movie studios' Digital Cinema Initiative selected a gamma of 2.6 as providing the best perceptual quality for 12-bit cinema projection" now in home theater.
Ted Dillard (11:19 AM on September 4, 2009; trimmed here): '... I think I got it from as near the "horse's mouth" as you can- Bill Atkinson, who not only pioneered ColorSync, but built QuickDraw and helped develop the first laser printer for Apple.
The story he tells is that they were trying to get the Laserwriter to print close to what the screen was showing- in monochrome, mind you, and the only way they could get it to work was to jack the gamma to 1.8. In his words... "it was the silliest thing."
Color Management wasn't even a thought at the time, and it set the stage for decades of Color Management mismatch and confusion. I asked him about it because I read a story about gamma, and that, back in the mid-90s this team took a bunch of cards and tested them- Mac and PC, and they all tested out to around 2.1 - 2.2.'Fun maybe just for me, I resold a copy of Bill Atkinson's photography book Within the Stone to Aardvaark Books in San Francisco last year; it was inscribed by a Bill Atkinson to the Dalai Lama.