So as I said I was able to find one such difference here from our internal communication.
WebChatbot got moved into base platform and is available for use by Platform customers (with no CS dependency). However, the CS team have taken the base web chatbot capabilities and enhanced them within the CS layer. So the CS flavor does more than the platform chatbot e.g. escalate to agent and integration with Pega KM.
There is no document which highlights the difference,but I will try to post if I find anything new.