I filled a form to IRS a while back about my question regarding W-BEN and tax for non-US Resident. Today, they emailed me the answer.

I posted it here because this is for every one of us who are not working in US and because the answer came from IRS, I will consider it comes from the most reliable source. I will save the email in case there is problem in the future.

My questions:
I am an Indonesian and have never been to US. I sometimes submit articles to US based internet company (like Associatedcontent and BrightHub ) where I gain little money (less than 100 USD) from upfront payments and google ad sense revenue. Usually they don t require me to fill W-8BEN form, but a new site I want to apply to require it. Should I fill the W-8BEN form? Also, I check that there is a treaty between US and Indonesian about tax exempt for Personal Service Income. Do I qualify for the tax exempt under the treaties, because I have never been in US and thus do not stay more than 119 in a year in US, and my income is not fixed? If so how do I tell the operator of the site I submit my articles to? Thank you for your help.

Their answer:
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Thank you for your inquiry dated October 16, 2009. We apologize for any delay in responding to your inquiry concerning if you should fill out the Form W8-BEN, (Certificate of Foreign Status of Beneficial Owner for United States Tax Withholding) and are you exempt under the tax treaty between the United States (U.S.) and Indonesia.

If a United States (U.S.) entity hires a nonresident contractor and if the contractor performs all of the services that he is paid for outside of the United States, this would be considered foreign source income or non U.S. source income. The Internal Revenue Service does not require the payer to report this type of income payment. Nor is this income subject to U.S. withholding tax. If this non U.S. source income is received by a nonresident alien contractor, there would be no filing requirement for them. Therefore the contractor is not mandated by law to supply the payer with the Form W8-BEN, but as a courtesy you may wish to supply the form to the payer. This would be a written document which informs the payer that you are not a U.S. person. This form is kept with the payer.
Because this payment is not considered U.S. source income and is not subject to U.S. tax, there would be no reason to take a treaty exemption. You may advise the payer of these rules.
Sourcing rules for independent personal services can be found in Publication 515, (Withholding of Tax on Nonresident Aliens and Foreign Entities).
Forms and Publications are available on the Internal Revenue Service web site www.irs.gov as well as tax treaty information.
We hope this information is helpful to you and thank you for using our service.
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In summary:

1. According to IRS, none of US resident person who is freelance contractor and working outside of US is NOT subjected to US tax. So we don't have to worry about paying tax to US.

2. W8-BEN is not mandatory under law, it is for the company internal record only.

Basicaly their answer is the same as what @michelledevon gave me, but coming from them, this makes it "official".