Interesting commentary all round. Ishtat had it right the 'Code' Documentary included many attemps to find technical, 'writerly' reasons why Christie's work has remained popular over the years.
"And then there were none", as a Play, has been running in London for 53 years consistently, as I recall from the program.
I sense some disdainn at my confession to having read none of Christie, add to that, no Sherlock Holmes, no Auther Conan Doyle, no horror books or flicks and I have never watched a single episode of Monty Python or the Simpsons.
Then again, I don't watch professional wrestling and I don't and never have frequented Bowling Alleys.
Personally I find the mystery genre, especially the formula type, to be utterly boring. I am however, curious to understand the current popularity of Vampire and Zombie stories and films as I see no value whatsoever in either.
I place the mystery and horror genre's in the same category as Soap Opera's, stories intended to entertain bored women during the daytime.
Amicus
Agatha Christie is like reading James Bond novels, Conan Doyle is part of the literary canon.