SEO - content - blogs etc and imagination is the only way to go for affs in many many industries.
Do you really think that a guy doing web hosting aff, can compete in PPC with the big boys paying $20 per click?.
If in the future online gambling is 100% legal, will be the same for us.
Maybe some profit from the long tier PPC.
The trick is than in every industry, there's allways something that the owners are not able to do. That is good information, reviews, news, recommendations etc.
It is not a surprise, that the sites doing very well in casinos are offering quality info.
After all, in the ebook industry there are guys running a megasite to sell only one product.