I encountered a company with an "antique" mainframe running an "antique" COBOL workload. It had 17 YEARS of continuous uptime. Every single piece of hardware was either double or triple fault tolerant, and nearly everything had been swapped along the way, but the workload (a transaction processing system of a sort) had never ceased operations. It had never needed to be changed.

I know mainframe != Win XP, but it is important to remember that in many systems, it isn't really like a car, where you do maintenance to keep it running, its more like a wrench, where you use it until it breaks, and then get another one that does the same thing. In the years that the wrench is in service, new types of steel, new ergonomics, etc. might come out, but none of that is sufficient reason for upgrade. Only the actual failure of the system justifies replacement. Sure, its rare for that to be the case in a tech company, but not so rare in a company that just uses IT to do something else.