Depending on the manufacturer the information below maybe usefull:
Some manufacturers will not supply a Recovery CD/DVD, HOWEVER, there will be a partition on the Hard disk which contains all the recovery information, most likely in the form of a disk image or something similar so if at any point the Operating system goes wrong or the customer gets a virus, he/she can simply press a button when turning the computer on to restore the said image from the "hidden" partition onto the user partition on the Hard Disk and everything is working as when the computer was first purchased. Some users actually like this simplicity.
The manufacturer will often provide a program which enables you to "Backup" the "Hidden" partition onto Cd's/DVD's should any faults occur with the HDD.
The manufacturer will often prompt the user to make these discs via pop ups etc.
If the customer decides not make the backup, that is their own choice, but if the HDD develops a fault outside of warranty or the recovery partition is deleted by the user while installing another OS for example, they will need to purchase the media from the Manufacturer which seems fair to me.