I am beginning to think that perhaps Palpatine does have a hand in Shmi's death. John Williams' musical score exemplifies this point somewhat. I believe Palpatine might have orchestrated Shmi's death because Anakin and Luke are supposed to have similiar life experiences, but make different choices. In ANH, Luke knows Uncle Owen and Aunt Beru were killed by the Empire (i.e. Palpatine) and instead of flipping out like his father, he decided to train to become a Jedi, but Anakin goes berserk after witnessing Shmi's death.