Google can't catch most paid links. They can't even catch large malware networks that have existed long enough to be reported in the mainstream media. But they can go after business models they do not like.
As Google tries to shift the web to improve user experience AND extract as much profit as possible, certain classes of information and information formats are rendered useless and/or unprofitable.
Web Directories

There are a lot of web directories that recently got hit, and those hand penalties are not the only way directories are being penalized. Google has been fighting off parasitic (or low value) link sales web directories for years by crawling them less deeply and caching their pages infrequently. Cache date is the new Google PageRank.
You can analyze changes and beg for forgiveness from Google, but they don't care about you or your site. They are only interested in improving general web trends, search usage, and their ad driven profit. This is not to say that analysis is bad, but sometimes we chose to analyze the wrong things rather than shift our approach to marketing.
An Alternate Name, Classification, & Approach

Domain names are worth so much because people tend to refer to you using what you call yourself.
Google's recent hate toward directories does not indicate that all directories are junk, but if you were to start a new web directory today what benefit is there in calling yourself a web directory? What if rather than charging $20 or $50 for a link, you charged much more and listed a real formal review on the site? Why not be a web review guide or a social bookmarking service or something else that is more in tune with the general direction of the web? Mahalo is worthless, but due to the different classification "human powered search" and associated public relations hype, it is much stronger than most directories.
Leverage New Information Formats

Ebooks are another concept that has got abused. So are many of the other classes of sites Google is going on record as saying you should avoid. The same types of information that appears in ebooks can be displayed using something like Sketchast, and be called something different, that is yet to be abused.
If you are in a competitive market your site should not be static. Even DMOZ created a blog.
Not All Arbitrage is Made Equal

If you are starting a new business it is best to tie your name and brand to a memorable, likable, and press-worthy topic. If you run a thin arbitrage type business the name and labels you use to describe yourself may be more important than the quality of your user experience. Spend upfront or pay later with limited exposure and/or a risky rebrand.


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