Wouldn't the market adjust for this fact? There is less demand for engraved iPods, therefore the price for them would be lower. If I was in the market for a used iPod, I sure wouldn't mind buying an engraved one if it was $50 or $100 cheaper than the non-engraved kind.
If anything, Apple is encouraging a used market, by artificially creating a lower-end used market.
If Apple really wanted to prevent a second-hand market for iPods, they'd do something like permanently lock an iPod to a specific iTunes account.
