Neither Sony, nor EA and Nintendo, explicitely dropped support.
EA's name , and the TV / Blue-Ray Sony branch, appeared in a letter asking members of the congress to act against piracy (without ever mentioning explicitly any bill).
Then, on the actual list of SOPA bill supporters, these companies were not present, making people jump to the conclusion they "dropped their support".
But :
* None of the 3 companies explicitly explained their position
* The 3 are part of the Entertainment Software Association, and guess what? This association is on the list of SOPA supporters.
This "Sony dropped SOPA support" is just a PR move, perhaps not even at the initiative of Sony themselves, but as I see it, they are part of a group supporting SOPA, and don't say anything about it? => they support SOPA
EDIT : A source found about this :
http://techland.time.com/2012/01/03/...-sopa-support/