I often ask the customer, how often does your server/network environment upgrade? Does your customer add new VMware/Hyper-V hosts regularly? New versions of Windows or Mac OS X or Linux? Unless the environment is 100% static, the customer is updating hosts and networking. Storage will need to stay updated as well, to address changes implemented by OS or hardware vendors.
If your customer is fine with never upgrading networking, OS or hardware, I think he's probably fine never upgrading storage.