WebProNews

* Google and the affiliate networks can and will co-exist. The affiliate market is completely different than simply PPC or PPA models. Lifetime for subscriptions, Views, etc in addition to the creative possibilities... so it is by no means obvious that Google will be a serious challenger here - or that it even wants to.
* Google's PPA offering is great for smaller publishers who are already using AdSense right now anyway.
* Larger advertisers want much more control and support than Google is offering. That's where affiliate networks excel and are clearly superior.
* Making affiliate marketing successful is about more than technology - it takes hard work and a hands-on approach, and that's not Google's style.
* Speaking of technology though, affiliate networks have developed highly sophisticated tracking systems that cover the vast majority of possible scenarios to make sure that partners/affiliates get paid for every qualified lead, sale, or whatever the commission model might be. Does Google have this level of sophistication in its tracking?
* Another point here is the scalability of various channels called multi-channel marketing. The today's sophistication of networs enables some players to manage all possible online marketing partnerships. This alone differs significantly from Google's overal objectives. Here I see them indeed making a pitch for an affiliate network, not only to get the horizontal reach but also to benefit from their overal know how.