The seller is in the US, therefore there is no US sales tax (similar to VAT) if it's an out-of-state or international purchase.
However for importing it into the UK, you have to pay the VAT to the UK taxman. Having said that, I'm not sure how many people actually do......
And no, I would never buy DVDs from Amazon US and have them sent to me in the UK without paying VAT - because that would be illegal.
