They might use an existing server, but that is beside the point. As a content provider they have no obligation to provide that service. Imagine if Direct TV did the same thing, would you cry net neutrality then even though they don't even offer internet services? What makes Comcast different?

I seriously doubt they have any obligation in their contracts with either HBO or the customers to offer HBO go on every device. My obscure settop box isn't supported (Popcorn Hour). Are they obligated to support that too? There's actually tons of set top boxes that aren't supported, are they in breach on contract for those too?

I didn't cry net neutrality at all, in case you hadn't noticed. 

That isn't the same thing. You're suggesting that HBO has to make the app available on every device, this is Comcast keeping it's customers from using it on a device that is already supported.