Earlier quoted context omitted.
What are you talking about? Microsoft is in the same market as at least 5 of those companies listed.
SOPA is largely an anti-counterfeiting bill. Microsoft does not want people to be able to buy counterfeit versions of Windows, so they support this bill. Google, on the other hand, doesn't make anything that can be counterfeited, so they have nothing to gain from this bill. They do have a lot to lose (with all the censorship provisions), so they are taking a stand against the bill.
FTFY.