If you look at heatmaps of user interaction with webpages, it absolutely does exist.

I especially like the Medium-like sites that force you to scroll over 50 cm of a huge image before some content appears...

The fold has existed in emails ever since people started top posting (I happen to think top posting is very often the best way to optimize your time spent in email).

Well it sounds like it does exist, in the sense that the whole article and the parent comment's experience suggest brevity has been working for them to maintain attention.

Unless you mean trying to pack as much in as possible without exceeding an arbitrary measurement of where the fold is, as opposed to just being very brief and to the point? If so, that does seem to defeat the point and would be inconsistent.

Emails always used to be written like memos though. There was even an etiquette that signatures shouldn't be more than 3 lines long.

I mean, it does exist, both on the web and in emails. And newspapers too!