What are the responsibilities of a Program vs. General Conference Chair?
Conferences in theoretical computer science like the ones you mention typically don't have general chairs. They have a local arrangements team for organizing the event, and program chairs to manage the review process. 

Many conferences in CS outside theory have a general chair because they have many more activities. The general chair might be in charge of selecting


The workshop program chair
The posters chair
The tutorials chair
Publicity (and social media) chairs
Treasurer 
Local arrangements 


And so on. The general chair can be viewed as being in charge of everything except the technical program and then delegates. 

But this may vary even within iterations of an individual conference.