That is changing.
Part of the rendering work going on today is the ability to render a page then analyze the rendering for a more precise understanding of the page. Predictive analysis is disappearing in this case. Instead, Google is working on understanding the rendered page much like we humans do- in a very real sense.
In regard to your question about content blow the fold.
The term(s) above/below the fold refers to one of the two major publishing print standards that web design has followed since the beginning- the newspaper (the magazine is the other). When a news paper is delivered and you pick it up, there is a header and some content and a fold at the mid-point that would mean that the newspaper would have to be turned over to read additional content. This is obvious of course. The most important content of any newspaper is what is presented to you first- the front page and above the fold. In browser terms, this means that once a page has loaded, the most important content is what is seen first and anything below the bottom of the screen (prior to scrolling) is less important. The fold in this case is the bottom of the screen regardless of the size of the screen. If a user has to scroll to see your content, it is said to be below the fold.
That will change soon.
Part of the rendering strategy is to become smarter about how a page is perceived in real world scenarios and to be able to further analyze the value of a site.
Content, even if you were not trying to please Google, should begin and have a fair portion above the fold for one simple reason. User experience. It is annoying to have to scroll page after page to read content or even evaluate if the content is what you seek. If your content is consistently below the fold, your time on site, time reading page, and pages visited metrics plummet. It is common sense. Do not annoy the user. Give them what they are looking for as simply and quickly as possible.
Google is seeking this too. Google is first and foremost concerned about the quality and user experience they provide their users. If they are able to increase user satisfaction with the first page of results, then they have a very happy user base. It has nothing to do with you and everything to do with Google's business sense. Google is a business and customer satisfaction is paramount. Satisfaction of the site that Google recommends is a major part of the user experience that Google provides. Content above the fold is a major element in web design that pleases users. It is that simple. Google is striving to increase it's user experience by measuring more accurately how you are pleasing the user.
So yes. Content above the fold helps your standing the search engine results page (SERP). And it will become a more important measure in the future.