That a Windows nettop "bests Apple TV in every way" is just your opinion, which I happen to disagree with.. Without getting into a lengthy off-topic debate on the merits of Apple TV.. Let me just say that I have 3 second-gen Apple TVs throughout my house. I use them as simple thin clients to stream several Terabytes of my centralized iTunes-served content. There is no way that a bunch of PCs can come close in simplicity, ease of use, and integration of my Apple TV based setup.
I'd agree with that, I tend to do the same. But it's not about Windows vs Mac per se. When you suggest to replace Apple TV with Windows nettops to gain an AirPlay cient.. I compare it to me bringing in my Porsche to upgrade to winter tires.. and the dealer saying - forget the winter tires, why don't I just replace your Porsche with this giant pick-up truck. Because I have been down the road of connecting Windows PCs to TVs, and it's as ugly as a giant pick-up truck. But YMMV