I guess my experience is the opposite ! :
- I tend to readily have original install discs. On every machine I ever bought I set up a binder, one per machine, with all the original discs, invoices, screen shots/printout of original configuration, keys, licenses, system recovery/repair disc ( and more recently the USB bootable drive for newer machines).
- I tend NOT to have original OEM drive and partitions as they have long since been replaced or revised
And yup, many versions of backups.
It only just recently I find the need to have to purchase retail version of Windows for my machines, when all else fails, or when Microsoft changes the rules of engagement, or vendor stop including media. Not a big deal. Can always rebuild a machine one way or another. Its data the matters and that's backed up a thousand ways