You all know Yahoo is merging with MS shortly for both search and contextual ad serving right?
Also MS is working on it's version of Adwords and Adsense via Adcenter and Pubcenter. YPN inventory will most likely just be merged into MS Pubcenter as the 6 platforms are merged
Yahoo Search merged with Bing results
Yahoo Search advertising merged with MS Adcenter
Yahoo Publisher Network merged with MS Pubcenter
This was a totally expected event.