It's not quite that simple... the spring pads, where half the car weight (less the weight of the axle and rear wheels) is transferred to the axle, are close to the tires and there are two of them. When you pick up the car by the center section at a single point, you're providing two bigger lever arms to bend the housing between there and the spring pads.
That said, everyone does it and they don't bend ;) Mine is back-braced anyway so I have no worries about jacking.
