I was thinking about this the other day, the problem is that we have only vertex groups. There are no edge or face groups (in sculpt mode there are face sets).
As the vertices of the centre faces are shared with the sides, the centre faces are selected as well.
Forgotten tools has a function to save face and edge selections.
But It would be good to have face and edge groups as well as vertex groups, that are available for modifiers etc.
oh thanks man .this forgotten tools is useful!