Why does my old table saw power switch cut both hot and neutral?
The technique is called double-switching. According to this article, on AC equipment the technique is used to avoid dangerous conditions when hot and neutral are reversed, as often happens with outlets that have been improperly wired.  It is permitted by this exception in NEC 404.2(B):


  404.2(B) Grounded Conductors. Switches or circuit breakers
  shall not disconnect the grounded conductor of a circuit.
  Exception: A switch or circuit breaker shall be permitted
  to disconnect a grounded circuit conductor where all circuit
  conductors are disconnected simultaneously, or where
  the device is arranged so that the grounded conductor cannot
  be disconnected until all the ungrounded conductors of
  the circuit have been disconnected.