It has nothing to do with that. If you look at pages to casinos, they will naturally rank for games with no backlinks, anchors or anything. They are simply given the green light by Google. For instance Sky Vegas in the UK. I personally know their "SEO Guy" is a joke, as he had me take down one of my sites because I outranked their own brand. Anyhow Sky will rank for a shit load of keywords position no1 with not one backlink to the page or game in question.
It has nothing to do with the money, the bingo niche went like this several years ago, barely an affiliate site on the first two pages. It looks like more and more gambling niches are following suit. As though one by one Google is working out the niches and pushing affiliates out. Plus these big casinos aren't as heavy into SEO as you would think, they rely on traffic from their affiliates, and not ranking their casinos.