Rmpi and Rprofile

At the top of the Rprofile file included with the Rmpi package, it
states

# Cannot be used as Rprofile.site because it will not work

Why is that? In the README file, there are instructions on how to create
an Rmpi script with R_PROFILE set to this Rprofile file. Isn't this the
same thing as using the Rprofile file as Rprofile.site?

Mark Lyman