If you think 20% is too high:
1. you haven't fallen in love with completely dynamic content, gotten past 'embedding single links'. try CGA for sidebars, wishlists, keyword lookups, post and page embedded product lists, now-reading style tagging, and the potential to build your own shop. And most of the embedding or PHP stuff is a single-line for big result.
2. you use a ton of OSS and never donate. :) :)
3. you're making a TON of money such that 20% seems huge, in which case you really should contact me on the side about just buying a commercial license outright. ;)
I've invested hundreds of hours (that's five figures if I was developing code FOR someone) in CG-Amazon and my other plugins, and don't think it's asking too much for people to either donate (i.e., 'get a license') or allow the 20% random links. This is for non-commercial uses we're talking about -- if you're trying to really make money, you should 'buy' a license from me.
As it is, I not only haven't (in 2.5 years) charged for use of my plugins, but I give a ton of support for them and wordpress, and even help people with custom installation, debugging, etc.
I'd LOVE if people would just support my continued WP development with donations or purchase of commercial licenses, and if enough people would do so, I'd probably move to a free use license for individual (i.e., not-profit-motivated) sites. That's likely the direction I'm headed with CG-Amazon 2.0 anyway.