Can RIAA Lawsuits be Blocked by Routers?

Chris Frank asks: "With the RIAA stepping up its pressure on internet sharers, what is the legal status of people behind apartment routers? With no logging of who is moving what who can the RIAA prosecute when it tracks a shared file back to that specific shared internet account? I would imagine that many Slashdot readers are behind routers that hold all of their internal IPs private to the outside world. Is the bill payer responsible for all of the users of that router? How can a person be held accountable for the actions of others, especially when there is no proof of who did what?"