The directions for running the sfc /scannow command...do not necessarily apply to "restore/recovery disks" since Microsoft doesn't produce such and the instructions for running the command originate (justly) from Microsoft.Recovery/restore disks
are provided by the OEM system manufacturer
who is responsible for system support...and these disks are manufactured by OEMs in a manner that many should not be construed to be the equal of XP install CDs (which are what should be used to run SFC).
Worth reading, IMO: How To Use Sfc.exe To Repair System Files - http://www.bleepingcomputer.com/forums/topic43051.html
Another thing to note...the CD used to run sfc /scannow must reflect the same SP as the system currently has. If the system has SP3 installed, you cannot use a CD which has less than SP3 included.