In New York (and, for all I know, everywhere else -- IANAL), city laws prevent you from signing away certain rights in a lease because shady landlords kept sneaking waivers in. For example, you can legally withhold rent if your landlord does not keep your property in a livable state. Many leases have provisions specifically waiving your right to withhold rent, but such provisions are legally enforceable.

There could be a similar law preventing anyone from signing away rights we deem too important to jeopardize.