New tech in the server space comes out slower than it used to. Moore's Law has almost dried up.
Fifteen years ago, you could assume that you would have 50% larger hard drives and significantly more FLOPS/watt with each year's new systems. Today, that trend has almost entirely stalled.
In short: servers used to have short life-cycles not because they no longer worked, but because they had so much higher operating expenses (electricity, datacenter floor-space) than newer models. That trend no longer holds; the more relevant question today is "how long will the servers work".
Fifteen years ago, you could assume that you would have 50% larger hard drives and significantly more FLOPS/watt with each year's new systems. Today, that trend has almost entirely stalled.
In short: servers used to have short life-cycles not because they no longer worked, but because they had so much higher operating expenses (electricity, datacenter floor-space) than newer models. That trend no longer holds; the more relevant question today is "how long will the servers work".