caperjack, if you truly wipe the hard drive, all partitioning information is gone and that includes your Recovery partition. If you have a wipe program that wipes individual partitions then I would agree with you but what has been recommended here is not that, it is a full drive wipe.
BFK, the op said "How do I reset Windows 7 to factory" then said "want to make sure everything is absolutely wiped clean before I ship this back". Can't have it both ways unless he has a Recovery DVD or has created the Recovery discs as Gregg mentioned.
If he wipes the drive he no longer has the capability of restoring to Factort state.