Without physical delivery there is no actual shipping address, so the states probably assume shipping = billing. It's just when there is physical delivery that the tax is based on shipping address. And as I stated, that's my experience.
This means that if you somehow got an Oregon address (Credit card to an Oregon address) you would be able to avoid paying sales tax on "electronic delivery" but it wouldn't help you if you were to be buying a new Mac from Apple. They would charge the tax based on the shipping address.
However there is always the chance that Oregon would pursue you for failing to pay Oregon income tax!