The issue is getting foreign sellers to stand under UK legislation - a statute is defined as a 'legistlated rule of society' - if you aint in the society then, fairly, why should you stand under their rules?
Where the distinction is blurred is when the foreign seller is trading via a UK marketplace or collecting payment via a UK agent, IMHO. I've won this argument before with a few arsey and threatening emails.... But, if you pay by credit OR DEBIT card, under the DSRs you are entitled to be reimbursed by your card issuer.
Chris