It's most clear in Britain where Received Pronunciation (eg, Alistair Cooke, the Queen, Tony Blair) is dead -- no longer even taught at Oxford and Cambridge. And it's happened only in the last 20-25 years. It's been replaced by "Estuary English" which really sounds horrible to my ears. The best example of Estuary English pronunciation is Jamie Oliver. It hurts my ears to hear him. I can't stand it.
Damned shame, too, isn't it!
He has a dreadful accent!