Web services Requirement at the client side in Orchestration

One quick question in [1]the Web Services Architecture as stated
under the section, "3.3.3.2.2 Orchestration", as follows:


3.3.3.2.2 Orchestration

<snip>
"For example, the seller must have web services that receive request for
quote (RFQ) messages, purchase order (PO) messages and payment messages. The
buyer role must have Web services that receive quotes (RFQ response
messages), invoice messages and account summary messages."
</snip>


How come the buyer(i.e., client) MUST have "Web services." The
client should be able to acess and interact with Web sevices
provided by the seller, i.e., the Web services provider, without
having Web services at the client side. I cann't think of any
scenario that the client, i.e., excluding the intermediary, need to
have Web services. Any comments?

Regards,


Pae


[1] http://www.w3.org/TR/2002/WD-ws-arch-20021114/#id2616565