I've read about it too.
Populations sleep patterns change over time.
Our cavemen ancestors probably slept all night because it was dangerous outside.
Our pre industrial forebears appear to have had a more segmented sleep pattern that presumably best suited their agarian lifestyle.
Since then industralisation and the advent of things like electricity have changed our sleeping habits further.
We can argue whether thats a good thing or not - but I wouldn't call 8 hour sleep a myth... and certainly not a scam :
D