How did you become acquainted with Roald Dahl's writing in the first place, Alex?
For those of us in the 'Commonwealth', or in the UK itself, it was a childhood thing (you know, he's much better known for his books for children, which are still good today), because his children's books were and still are, to a certain extent, wildly popular here and there.
And then, as you get older, you realise that he wrote all these fantastic stories which weren't aimed at kids, too!
Personally, I think he's one of the best things that came out of British writing in the 20th century. And while he was educated in the UK at the insistence of his father (his father died when he was young, but his mother, at great personal cost to herself, abided by his wishes in this regard), he was racially a Norwegian! I think there's a moral or object lesson in there somewhere.
I know he was also popular in the US, and actually did a lot of writing for periodicals in the US, but I always thought his readership was much smaller (per capita) in the US.