How long should online articles be?

Zainab Zakari has penned This article is 1,689 words long for the New York Review of Magazines, reporting on the various theories concerning how long articles should be online. Mentions various studies on attention spans and anecdotal evidence of why 1,000 words is an arbitrary and incorrect benchmark.

"Weisberg chose 1,000 words arbitrarily, but he and Nielsen are echoing the prevailing wisdom that, on the web, shorter is always better. If you don’t keep it short, you’ll lose the reader’s attention—and once a reader is bored, all it takes is one mouse click to kill an article.

Are these assumptions justified? Based on my personal experience, an informal survey of the literature in the field and conversations with various social psychologists and social scientists, I believe they are not."