Re: keeping swappable spares in stock might make sense
The problem is that the decision NOT to buy spares is always made when the kit is first installed, spares are plentiful and the number of processes running on it are not too bloated, so cost of downtime isn't too great. So a beancounter looks at the numbers and veto's having spares because "the cost outweighs the benefit".
Give it a few years and all those processes have grown in importance and a few got added. Meanwhile the manufacturer has come up with new shiny, shiny kit and the spares for your stuff now have to come from the "long term support center" at triple the cost and four times the delivery time. Downtime is now absolutely killing and guaranteed to be 4 times as long, but since the beancounters originally calculated you don't need spares, you can't have spares.
Biting the hand that feeds IT
