Withdrawing under fire is the standard tactic employed to give the impression that those doing the firing are the victors. Nothing new here.
In my humble opinion, Gaza was Sharon's sacrificial lamb in order to try to convince the world that Palestinians are too backwards and ape-like to be trusted with territory formerly ruled by Israel.
His hope was that Gaza would fall into utter chaos and disaster, and this would be used as an excuse to never leave most or even a majority of the West Bank.