[30% rule] US driver's license -> Dutch license

Dear Americans in the Netherlands:

I have a question about exchanging the US driver's license in the Netherlands based on the 30% rule. I went to the municipality's office to exchange my license (with no exams), and the process went just fine. At the end, however, the officer said that RDW would not return my WA driver's license.

I'm wondering how US licenses are dealt by RDW. My Japanese friend in the Netherlands told me that RDW sends all Japanese driver's licenses to the Japanese embassy in the Hague, and the Japanese people can pick them up at the embassy. I read the US embassy's website in the Hague, and they clearly state that they are not anything to do with the driver's license since they are issued by states.

Is there any American or US driver's licence holders in the Netherlands who exchanged the driver's license before? Did you have to reapply for the US driver's license in your state? Is there any way to get it back from RDW (I tried to attach a letter saying "please return my US license", but the municipality officer REFUSED to add it to the application)?

Thank you.