The machines did not just imprison humans for energy, its symbolic!

I think many people don't get the animatrix and the whole human/machine connection. I believe that the machines didn't just need there energy, I believe the machines have this connection with the humans that they want to be like them, hence programs like rama kandra and the oracle who are very human acting and programs both in the matrix and machine worlds seem to want to emulate humans, since they are there creators and I think this is part of why they keep them alive if only in a comatose state. I think its mentioned at the end of TSR that this was a symbolic joining and man and machine together. I'm pretty sure that is also the meaning behind it. the machines certainly have some kind of emotional attachment to them.