I'm thinking about this...a Faraday cage needs to be grounded...and it also doesn't allow EM signals to pass through...I think cars and planes fail on both counts. Well, a car is grounded but not well grounded. But I can definitely make a cell phone call from inside each vehicle, so EM can pass in and out.

Cars and planes may survive EMP, but I think it's inaccurate to say it's because they are natural Faraday cages. The electronics on both are shielded against normal EM interference, and that may be enough to save them depending on the particular EMP.

Actually, aren't most open-mesh Faraday cages insufficient to protect against EMP, although they may be sufficient against things like lightning? I know I read that somewhere.