It's a good question, to which there is not really a good answer.
News / article sites often break up their articles into pages on purpose, so that if a user wants to read the entire article, they will automatically generate a lot of page views (six+ per article), thus racking up ad impressions.
Second reason for breaking up articles into pages is because supposedly people prefer their articles in bite-sized chunks, for example for staggered reading (one page at a time with breaks in between). More recently, a trend the other way has been forming, with people preferring articles on one page. I'm not really sure what people prefer.
There's also performance and bandwidth. If you have a long page, it'll take a while before it's loaded (the html / text), and quite a bit of bandwidth if you have a lot of images on there - even if they're Wordpress-generated thumbnails. I've seen a few 6+ MB articles / pages on TLS when I was checking it out. More advanced sites - tumblr, for example - have employed a 'load on demand' kinda thing, where stuff like images, but also posts and things like related articles / footers are only loaded when they come or about to come into view. Which is fancy.
There's a setting in an optimization module we use that will lazy load images, i.e. only download them when they come into view. I switched it on to try it out earlier, but the experience was quite jarring (think images popping up when you scroll down) and I'm not sure if there's an overall benefit.
tl;dr: I'm not sure,
. I'd say ten or even twenty-paragraph posts are fine to put on a single page, but longer articles and articles with a lot of images are probably better to be split over pages for performance reasons.