When a knife / slicer blade goes through the outside of the orange, any bacteria on the outside can be transferred to the inside, so in theory, the outside of any product you cut into, whether you retain the outside skin / peel for consumption or not, should be washed. In practice, I don't wash fruits etc that are going to be cut and the outside discarded (say, avocados). Nor did I routinely see oranges properly sanitized (or even rinsed, which isn't going to cut it germ wise anyway) before going into those machines (or when juiced by hand).