Actually most servers and systems sold are designed for exactly seven years. It matches the standard IRS amortization schedule. The sales guy will be on your doorstep the day you no longer can depreciate the machine.
Some companies are moving to three year amortization, but not many. Usually the ones in fiscal trouble do it.
I have numerous Linux servers at work that are older than seven years old. (And one hasn't been rebooted in 1227 days as of today.). We're in the middle of a hardware refresh and the new machines are way overkill. We should be doing more virtualization, but there are political and just plain stubborn people who are blocking it in many ways. More boxes, more work for me to do, (which I mostly script anyway) so I just politely disagree and carry on.
Some machines are very capable of running that long. The hard drives, no. Fans, not always. (Ball bearing high quality ones will if kept clean.)
And there are some mid-range enterprise and mainframe folks who'd also disagree too. That stuff gets installed, turned on, and runs for decades. Blade servers too.
In telecom, seeing a 10+ year old Sun server was very common. Suns were built as servers, not as desktop hardware shoved into a rack mount case... but pricing trumps quality and Sun stuff is spendy now and not popular. Especially after Oracle bought them.
It's not always the hardware that needs replacing, it's the never ending merry go round of forced software obsolescence and lack of official support from vendors designed to force you to continually upgrade, which are the limiting factors for businesses.
If you have people willing to maintain older systems and OSs that allow that... running older hardware and just swapping disks regularly is ultra-cheap and can make a significant bottom-line impact.
Microsoft as a general rule, doesn't operate that way.
A side note for the original poster... SCZI... Is actually SCSI. Small Computer Systems Interface. Pronounced "scuzzy" by most folks, your mistake is completely natural. No big deal.