Legend says that back in the mists of time, when the first UNIX was created, its developers needed a low level command to copy data between devices. As they were in a hurry, they decided to borrow the syntax used by IBM-360 machines, and to later develop an interface consistent with that of the other commands. As time passed, everyone used dd and it's odd syntax stuck. I don't know whether this is true, but it is a nice story to tell.