Actually, it's more than two. We have gravitational, rotational, and acceleration stresses to be distributed around a strangely articulated structure.
Nothing gives more rigidity than a cylindrical wall, anchoring tensioning cables and supporting struts in a radial configuration. The tiled surfaces have just enough give in their flexible sealing gaskets to be able to adjust along with the redistributed stresses.
Even with all the strength that our supporting arms have, we find it expedient to use tensioning cables to reduce wobble and help to balance the forces. In many respects, it's like an old-time sailing vessel, with some lines secured, and others belayed, and tremendous forces played against each other.
indeed. I left out the liftoff, drive, and rotational stresses as relatively minor in comparison to the gravitic and PSI stresses... but "relatively minor" does NOT equate to trivial.