No seriously, why would anyone need to hide their IP address from their financial transactions?
Because we want to be... anonymous.
But why?
Because your ip address goes directly to your internet connection, ie, your house, place of work, etc... So even if your wallet address isn't traceable, you are still exposing your ip address to the network. If someone is recording that information, they can follow a payment directly from you to the person you paid's address. This information is not being recorded on the block chain, and it would take someone on the network logging this information to get it while it's happening, but still, we don't want any holes because holes get ripped open after a while.
"Just as you would address a letter to send in the mail, computers use the unique identifier to send data to specific computers on the inter web. "
Yup, just a call to your iSP and they can ask who had this IP address at this time on this day, and they can say exactly who