Their complaint: that pharmacy benefit managers, which design health plans for companies and insurers, offer retailers a take-it-or-leave-it contract that makes it impossible for them to compete on drug prices with mail-order houses.
If an act of nature, a specific supplier or some other uncontrollable act can make it impossible for you to fulfill a contract (and thus open yourself up to legal action) then you should be putting to ink that you are not liable for incomplete work due to these factors.