I think you mean EPC (earnings per click). And is that really true?
First of all, nobody but Google knows what the payout percentage is for any given site. So how could Yahoo "consistently pay out higher than Google"?
Second, Google's overall payout to publishers is nearly 80 percent, and it's hard to see how Yahoo could exceed that figure by a significant margin for any length of time without making stockholders and Wall Street analysts unhappy.
Third, even if Yahoo accepted losses or minimal profits from YPN during the recruitment phase, how would it retain publishers later on when it adjusted the publisher payout downward (as it would have to do at some point)? Publishers could abandon YPN just as quickly as they could abandon AdSense.
This brings up the question of which comes first: the chicken or the egg. As a publisher, I'd rather have targeted contextual ads right now on my hundreds of subtopics (which Google can offer) than wait for YPN to build a larger network and attract more advertisers.
If YPN wants to compete with AdSense, it will need to offer innovative advertising products, not just me-too products with assurances of higher payouts.