laws are most likely different in the US than in the UK but the companies here must comply by the same laws as the rest of us. you can in many cases get a case dismissed on the slightest technicality.
using the "unsecured" wifi excuse is working for O2 customers in the uk who are getting sued for huge amounts of money from ben dover productions
And perhaps most crucially the letters cannot hold the bill payer liable if someone else used their internet connection to download illegal material
the citizens advice is a wonderful service
also good news for those in NY
IP addresses alone not enough to lay blame on an individual (piracy related but same principle)