They were physically there, they have every right to purchase them. How you decide to deal with it at the border on arrival back to the UK is the issue.
But Delaware has no tax....
OK what about all of the random things purchase from eBay hong kong sellers that are under the £15 import threshold? Is that some for of theft?
When I was watching anime I purchased a Huge amount of DVD from US, Japan, korea and other countries. It wasn't very often I got charged import tax/duty. Even when I was the majority of it seemed to the the RM/courier "handling fee" rather than the tax that went to the government.
Back to my example above, if this was a physical collection people were buying from amazon there would still be no tax/import duty and no revenue going to the UK government as its under the £15 threshold.
I really fail to see why so many people are getting in a tizz.
Would it make you all feel better if I got my american friends to buy them for me and they then give me the keys ?