The title is somewhat misleading. Think of it like "Venn diagram intersection of Netflix Instant and IMDB top 250".

Good catch. The Godfather (imdb: 2, 3); Shawshank Redemption (imdb: 1); The dark knight (imdb: 1) are not available on instant watch. The blog post says "All the IMDB 250 that are available on Netflix Instant.", not "IMDb Top 250 available on Netflix Instant" as the HN post (which I interpreted as all 250 movies).

Because they aren't available on Instant Play.