SOPA has not passed and now probably will never pass. What happened last week to MegaUpload had nothing to do with SOPA. The grand jury investigation into MegaUpload began in 2010 and the FBI investigation in 2008, long before SOPA was even drafted. The grand jury indictment was handed down several weeks ago and only unsealed last week because of the arrests, which have been in the planning for weeks.
FileSonic is not afraid of SOPA because SOPA is not law. FileSonic is afraid because it has servers in the US and is thus within US jurisdiction.
FileSonic and FileServe's recent action to stop third-party downloads is pointless legally and, if anything, subjects them to greater legal liability because they're tacitly admitting they were doing something wrong in the past. It does not protect them from criminal prosecution. One major portion of the Department of Justice's case against MegaUpload deals with a practice they stopped last year -- paying for downloads. They stopped the practice on their own, but that doesn't prevent prosecution for what they did before they stopped the practice.