Pet Peeve

It irritates me when someone pays for shipping/tells amazon the item has shipped when the item hasn't shipped yet. Amazon told me the seller shipped the item I ordered on the 19th, according to USPS and the tracking # USPS hasn't received the package yet. I understand buying postage early I guess but I know from selling on Amazon that you have to click a button saying the item has shipped... Why do that if you haven't actually shipped the item?