Exactly, you'd be liable for the loss and they wouldn't. In fact, I'll bet they don't cover the nonmedical portion of such a loss at all.
Fork lifts are rated by the manufacturer using a bunch of criteria Dan. These ratings reflect the balancing act between build cost and the cost to build to the max capacity of the strongest component. There are also huge overbuild/derating premiums built in to account for degredation over time. Most fork lifts will handle twice their rated load but you will have to put back some of the mass removed by the original design team to get an acceptable service life out of things like the suspension and steering systems.
Got it? The big risk is tipping the thing over or unexpectedly busting the steering gear, not mast or fork failure. Stability is a given within the rated limits. Exceeding those limits makes them unstable to the degree that you push the actual lift to failure capacity of the system. That's the key, these are systems - just like your machines.