It corelates to value derived from the page.

SO the people I deliver the most value to, I extract the most value from. // WIth an added bonus that I recieve more value from the people with more expensive computers (aka the wealthier viewers)

I don't see how the time spent on a page correlates to value for the reader. If I read faster or slower than someone else and spend less or more time on the page, it doesn't change the value provided to me by the article.

On the other hand, if a site provides more value to a visitor, they are more likely to keep spending more time on the site.