I have confirmed this myself. As of now (June 2009) you CAN NOT cancel an iTunes account. It is recommended that if you want to stop using it, you remove the credit card information off of it; then ignore it. You should uninstall iTunes from your system after that.
You can abandon the account and create a new one later. If you want to talk to an Apple representative, please call 1-800-SOS-APPL or 1-800-MY-APPLE
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