For the same reason I gave when I answered your question from three days ago.
I wrote:It's a class that delegates to an underlying HttpServletRequest. It can be used in any number of ways to provide additional functionality.
For example, it could be used to handle multipart requests automatically, provide additional functionality to JSP EL (in S2, for example, we first use default attribute lookup--if an attribute isn't found we check Struts 2's value stack), and so on.