Apple is missing because they're usually on both sides of everything as a media provider
Wikimedia? Considering they were very vocal about SOPA, I wonder why they are not a part of this.
I guess Microsoft doens't think of itself as an "Internet company", and they've often been on the other side of bills such as SOPA, etc, at least before the backlash.
It makes sense if you consider where their main revenues come from: Windows and Office, desktop products. Windows 8 features tighter integration with Internet services, but by and large they are firmly rooted in the idea that your desktop should be doing computation locally. The minute Microsoft calls itself an Internet company is the day that desktop software goes the way of the dinosaur.
twitter
Apple?
Netflix
neither is Amazon
if you look at the actual IA website you'll see amazon is there :)