The advertisers don't need to know a thing about me, they just need to know the general demographics and interests of the publication.
For example, the ads on this blog[1] are far more relevant and less invasive/annoying than anything that Google ever showed me before I started aggressively blocking ad networks. I assume that it is because the blog knows what I am interested in better than Google does, simply because I voluntarily go to their website and read their content.