Can iCloud do two-way photo syncing (deletion) between the iPhone and a PC?
As per the requirements and criteria of my question's description:


  The premise ... is that after taking dozens of shots ... and then deleting the ones I don't
  like ... I'm not left with ... photos on the iPhone device
  which I no longer want.


I can answer that NO, Apple does NOT provide a way to two-way sync iPhone device photos. iCloud's two-way syncing between a PC and an iPhone only works for the 'My Photo Stream' folder. What I was looking at on the iPhone, where I was not seeing photos being deleted by PC two-way sync, was the Photos tab in the iOS Photos app - the default view of the Photos app when the user first starts using iOS. This is actually the Camera Roll folder, and there is no way to do two-way sync with these original iPhone images on the device using iCloud (or any other service).

However, to answer the question's (more open) title itself: YES, Apple DOES provide two-way sync between the iPhone and a PC, BUT only for sharing/syncing selected photos from the device (and only for 30 days at that) - NOT for editing, or managing the original set of Photos on your iPhone device. To see the (near simultaneous) two-way sync in action on the iPhone, go to the Albums tab in the Photo app where in the My Photo Stream folder you see as it currently designed. To manage or delete original photos themselves, you will have to manually delete and edit them via non-cloud-syncing methods.