Maybe you don't understand because judging the value of a listing on how manipulative it is of SE algos may not be the only reason to list! Targeted Traffic!!!!!!!!!! Which is 10X more important than manipulating link algos. YellowPages work because:
1. they drive targeted traffic IMO, converts well ahead of Yahoo!
2. they are at the top of many SE results local or otherwise
3. They provide backfill/distribution for major local directories like Google maps (yellowpages.ca)
4. YellowPages get billions of searches a year by people who are more likely to be in buying mode

I agree the listings are absurdly expensive... consider a one month listing on idearc is almost equal to a year on Yahoo!. Buy the PPC! The listings seem more expensive than the PPC (my experience is in Pay day loans), but the listings are being distributed so that may change. I also found the PPC converted a little better!

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Follow me on Twitter! On the Trail with SOSG How I became a Social Media Convert and Twitter and Agents of Influence and now regular poster at Cloudmixer where We're Mixing New Media Ideas.