When people claim to be making big money from affiliate links, it's rarely Amazon links (or, rather, Amazon doesn't make up the lion's share of the income). It's affiliate links to products on Clickbank, joint venture promotions (e.g. all the JV partners who helped sell Frank Kern's Mass Control), or links to other vendors or middlemen that pay better than Amazon (e.g. Chitika or Web hosts).

I know someone who - until Google really started clamping down on it - made about $10k a month as an affiliate for a major text link ads company merely by running ads on Google Adwords for them and getting a payout when they signed up.

Back around 2003-2004, I worked alongside an affiliate marketing department at a bargain basement Web hosting company that paid $100ish per referred signup (which was amazing since their account only cost about $100 for the year anyway). Some folks (often with "web hosting review" sites) were doing hundreds of referrals for them each month. It's a big business, but people don't tend to shout about it.