I think you will find, it's becuase the Dutch watch American films and series etc without any dubbing. They put sub titles in Dutch. So consequently they learn to speak English with an American twang so to speak.
However if you take countries like France and Germany, they dub (or used to) the American accent and voice over with their own language and use american subtitles. It's really weird to see the stars speaking so fluently in a foreign language, whilst mouthing in the American language. Spoils the films completely.