I hate to jump on the bandwagon but more than just online killing the high street, it's one in particular - Amazon.
HMV have an online presence selling everything they do in the shops, they just cannot compete with Amazon.
Even Play have struggled in recent years.
Until the Government forces companies operating in the UK to pay UK tax foreign companies (read Amazon) are going to continue to kill off the British high street.
I don't think the all-under-one-roof, bulk-discounted approach of the supermarkets helps high street retailers either - if you can drive to a convenient out-of-town Tesco* or Sainsburys with umpteen parking spaces and stuff your trolley with paperbacks, DVDs, etc. as well as groceries then convenience-hungry shoppers are going to give town/city centres a wide berth.
Since the whole tax business came to light, I've stopped using Amazon and would rather purchase on the high street and be served by an actual person.
*I'm not a big fan of Tesco on many levels; apologies if my excessive criticism of them is starting to sound like flogging a dead horse.
"Not so much a religion as a savings club for people who think Star Trek's a documentary"
- Marcus Brigstocke on Scientology