When purchasing through the web store, you actually purchase from an American company called ‘eSellerate’.
eSellerate are a US-based company who are registered for VAT in the EU, and their VAT ID is shown on the bottom of your order confirmation with an ‘EU’ prefix. Business customers should enter their EU VAT ID during the purchase process to prevent VAT being charged.
Further information on this can be found on the eSellerate web site:
Hope this helps, if you have any further questions relating to this please contact eSellerate directly at: firstname.lastname@example.org quoting your order reference number.