Expression author versus provider of policy expressions

http://www.w3.org/TR/2007/WD-ws-policy-guidelines-20070928/

The three bullets in section 1 talk about roles other than an 
assertion author who may find the document helpful.

What is the difference between the 1st and 3rd bullets? That is, between

1.  WS-Policy expression authors who need to understand the syntax of 
the language and understand how to build consistent policy expressions, and

3.  Providers of policy expressions who need to understand how to use 
the assertions authored by Assertion Authors


Is not the expression author the same as the provider of policy expressions?

Paul