1
We cannot prevent that an author acts stupid and submits a later version of the same paper erroneously as a new paper, because we cannot check the semantics of the paper.
2
This does not mean that there could not be predefined topics.
3
Typically this is the case, if one sees that it's a paper by some friend/colleague ...so that one fears that one does not have an unbiased opininion.
4
In general a paper gets reviewed by more than one expert.
5
For the discussion we ignore the fact that there might be equal outcomes.
6
Whether it's wise to act as a dictator, overruling all the others in the committe, taking lonely decisions, or undoing decisions taken in consensus is a different question and outside the possibility of our modelling.
7
Note that those semantical changes of the chair are different from what the administrator could do. The chair should be able to make the changes within the software, while the admin in some sense is outside. The admin can probably also change data, for instance by directly querying the data base (or wiping out the data base from the file system, for that matter ...) but that's something else.