I'm not sure about the 2nd part of your comment - rims are designed for external force pushing towards the center, plus the mass of the bike and your body is spread out over much more rim surface area (and across 2 tires) between the rubber contacting the rim and the amount of surface in contact with the road. The design of the rim could also affect this, a rounded inner rim protruding toward center would have a small single point of contact, while a flat rim would again spread the load a little. The pulling stress is different - I don't think it would be that big of a deal anyway, but it could more easily affect spoke tightness and as a result of that make your wheels out of true and less safe to ride.