When did you last have to replace a CPU or a DIMM?
Silicon chips are amazingly reliable. I see a DIMM that failed in service once or twice a year (8 or 16 chips per DIMM, 2 or 4 DIMMs per PC, about 400 PCs). And I suspect most of those failures are with the soldered joints onto the PCB, or with the connector.
I've seen a failed CPU twice in twenty-plus years. (Maybe a few of the old boxes that went straight to the scrap-heap were CPU failures rather than MoBo failures, but either way they'd lasted well into obsolescence).
At this level of reliability, a stack of 100 will still be acceptably reliable. Possibly, more so than the same 100 chips soldered onto a board (which you don't repair anyway in most cases).