Hemingway said that? I'm Shaw that I heard it was Bern, before Ern.

But to return to the subject, I don't get to view the adverts from US TV, but would guess that the voice-overs are largely done by your own citizens using what they believe to be 'the British accent', rather than by actual Britons.
Their problem (if there is one) is that accents here are many and various, changing noticeably over as little as a mile distance. Some are decidedly unpleasing, others quite musical. A further problem is that after years of attempting a degree of consistency (BBC English, received pronunciation, educated accent or whatever) our broadcast media have attempted to get wiv it by promoting the use of regional accents without distinguishing them from mere lazy speech patterns affected by the yoof element.

Mind you I get a giggle out of hearing toffs who wish to gain credibility among the unwashed masses they despise, catching themselves about to pronounce a T, and hurriedly gulping-in a glottal stop. Politicians (no names) are particularly prone to this one.