The huge amount of Amazon affiliate pages are the result of so many people using scripts such as the Amazon Products Feed (APF) which allow anyone with a web site to basically sell every item at Amazon. Google seems to like these pages, and many times will index tens of thousands of "pages" which were generated dynamically from these scripts, and therefore a lot of them show up for search results - especially when you do a search for a particular product that Amazon carries. Luckily this trend is starting to slow down, as Google is starting to penalize all these sites with basically the exact same content, and therefore their position in the results should drop, hopefully bringing more relevant pages to the top of the results.