Now I know why patent attorneys are trained lawyers. A patent isn't so much about invention. Its about owning a territory and arguing that territory should be as large as possible.
Since invention-space is non-Euclidean, there is always some more space to occupy with your invention than is first apparent. Although, this largely depends on your attorney. Finding this own-able invention-space has been an interesting journey these past few years.
Through working with my attorney, I also learnt that the USPTO also has deadlines and targets making them amenable to negotiation. Its in the USPTO's interests for patent applications to be abandoned or approved, the middle-ground of arguing back and forth is like purgatory for you, and the agent handling your application. Since the USPTO can't force you to abandon an application, they have to negotiate.
On this note, we've been negotiating with the USPTO and are looking to have some good news soon!