Interesting, I'd find that super annoying as a consumer that's used to seeing the full price (ex. delivery) upfront. Is this standard practice for online US stores?
As always, US pries are ex-tax (meaning state sales taxes are added on and can be as much as 10% depending on city and state). Most other places (UK included) as inc-tax. If you take out the 20% VAT you get to 349 GBP, which is ~437 USD at current exchange rates. That's not that far off.