"I would ague that as a practical matter, it should not matter whether the buyer buys the product and then pays a business to sanitize it versus just having the service put in before it is bought. There is no real distinction from a practical standpoint. There may be the legal distinction, but the legal distinction is moot when as a practical matter it can be done the same way (I could buy the DVD and immediately ask the seller to alter it for me)."
Here's the problem: The modifier of the DVD has to either modify and edit a copy each time the customer requests it (that might be legal) or he has to create a modified master to use in making duplicates. The master, itself, would be an illegal copy, because it is not for the personal use of the owner.
The cost of individually editing each copy would be prohibitive, but the duplicator could not legally create a master copy to be used in making those duplicates for a fee, since that would not be personal use.
Legal nitpicking, certainly, but that's the nature of the law.