Tax form and payments.

Hello,

I have questions about tax forms and payments. As you know most of CPA/PDD request W-8 or W-9 tax form but why they need it? Yesterday I contacted one non-USA network and they said that they don't need any forms filled.
I'm curious how big and small CPA/PPD companies manage their payments to affiliates? Do they use any service?

Any non-US company will not participate in the US tax system, so they won't need the forms...