Unfortunately its a simple fact of life that if you have a great idea, or you are successful, others will copy it. Its one of the first things you learn in business and the only answer is to evolve faster than your competitors and stay ahead of the game.
Search Engines and the Internet in general, hell technology in general, is still very much in its infancy and until such automated technologies can replicate the human brain, there is little chance of parity and fairness, particularly when it comes to the Web.
Some people take the “if you cant beat em join em” approach while the more astute evolve their businesses and keep one step ahead of their competitors. Anyone looking to make a living from being an affiliate, or have become dependent on the income, needs to have a business plan and targets. It should be among the first things you do if you are not just treating it as a hobby.
But hopefully Google et al are working their way towards providing the results you’d expect from a search engine where sites are manually reviewed and priorities are based on content. It may get better but just don’t expect it to be aywhere near perfect in the next 5 – 10 years or so.
Just my $0.02 
Cheers
Simmo!