Just b/c someone (DLR) puts it in a contract, doesn't make it absolutely binding. There are many many contracts, or parts thereof, out there that can be non-binding, yet ppl see it in print and think it is the last word on any given topic.
I hate to say it, but at my office, we issue a contract of liability, and I know for a fact it would never hold up in court if it ever got to that point. We use it to deter ppl from acting foolish. Ya know what? It works!