When people ask, I always explain the Dutch skills in the English-language as resulting from the fact that the Dutch watch a lot of television and all of it in the original language. That means a lot of British and American series on Dutch TV, all with subtitles. Even children are used to subtitling rather than dubbing, and this also contributes to their reading and writing skills.
But all that's about to change. In the last few weeks, the Disney Channel put in an appearance on the Dutch cable network and has taken the unparalleled and awful step of dubbing English-language children's programmes into Dutch. No more reading subtitles whereas in the past, even 6- to 8-year-olds had some English skills because they had been subjected to a diet of the Olsen twins and Batman.
So it'll be a great relief to English native speaking translators like me that the Dutch are about to see the quality of their English plummet.