The lesser of two evils
Given this sorry state of affairs, you basically have two options: Either you purchase exorbitantly priced mission-critical support with a service-level agreement that stipulates a time to resolution -- not response -- and hope it is honored. Or don't count on the support at all and build in your own redundancy.
That second option has become increasingly attractive to many of the clients I work with. Why buy one fallible device and spend half as much again trying to guarantee it will be properly supported when you can buy two for slightly more -- and perhaps implement some geographic redundancy at the same time? With devices lower down the food chain from primary storage, it's common to see a raft of hardware (such as network switches) covered by the lowest-level warranty and protected by a spare device sitting on a shelf.
Whatever your approach to covering yourself, you'd better have one. Unless you're absolutely confident in the SLA that's being offered, don't take a vendor's promise to support you within a certain timeframe as a real solution for maintaining uptime. If the vendor doesn't follow through, you're the one who has to deal with the consequences. Having your own do-it-yourself plan to resolve things quickly -- and follow up with support afterward -- is often the best protection money can buy.