Unless you were recently dealing with a repair requiring that size drive, the mistake could have been more complicated. Hard drives did not always use 1000 as incements for size. Originally, before creative marketing took advantage of SI units, the drives were measured by actual data capacity. Perhaps your purchase was a transition period and the owner was looking at the CHS to determine the data size verses the marketed size.
I know at the time they changed how the claimed size was created a lot of confusion. My toshiba laptop with its enormous for the time 2.1 gig harddrive was actually a smaller drive using compresion to be reported as larger. Toshiba ended up replacing the drive in 1997 or so because someone was suing them. But i only found out because the CD rom needed waranty repair.
For all intents and purposes, the switch to SI happened way back in the 80s when IDE first came out and you didn't have to go enter in bad sector lists into the BIOS anymore. Heck, you probably can remember shopping for hard drives and looking at the bad sector list to find one with the least number of them.
Of course, in those days the capacity probably included using the bad sectors as well.
But the use of SI units has been around forever, when even just writing the number of bytes out was doable. (I still remember the WD press release when they announced IDE).
And I recall plenty of ads that stated "1MB = 1 Million Bytes" back in the way early 90s.
Of course, this cheat is somewhat handy for SSDs where you cannot use every byte because of FTL and other overheads in the system (including 2% bad block when new overhead - yes, up to 2% of flash can be bad from the get-go - so that 128GiB flash can have 2.5GiB in bad blocks).
Anyhow, I've had this situation happen to me - a store I frequented accidentally sent me an item I didn't order. They offered to refund me for shipping, or I could buy it at a step discount (this was like a $130 item, they offered to sell it to me for $55. Or I could send it back.). Now, I know it wasn't a scam since I dealt with the store before (and they have superb customer service), and the guy even admitted that after the costs of return shipping, $55 was about all he could hope to recover in the end. I just bought it - $55 for a $130 item including free shipping? That was a steal (and I was eyeing the item anyhow, being offered to me discounted, free shipping and in my hand now? Icing).
And I know of other stores that did the same thing - they shipped us too much of a USB3.0 card, and said we could keep it - it was a $20 item and not work the whole RMA and return shipping thing.
Of course, I was dealing with well trusted stores.
Heck, Amazon did it to me too - they switched to a new shipper and who misdelivered it. Amazon shipped a replacement and a week later, the misdelivered item arrived. I called Amazon up, they sent me a return label and everything. I went and shipped it back. When I noticed they accidentally credited my account, I called them about it - they were so kind they removed the partial credit (Amazon charged $6 for shipping -taken out of the refund), and I then realized I got the items for free. I called them back and told them, and the customer service just shrugged - they really didn't have the power to fix it, and the costs to do it all would probably have exceeded the item cost (around $40). And yes, I admitted to them I wanted to be honest and pay for the stuff I got (it was their mistake, after all).
In the end, I got free stuff, deeply discounted stuff, and a clear conscience knowing that I at least tried and got permission. Free stuff is nice. Free stuff legally acquired? Even better. And companies that know their business well know when to cut losses and when to pursue.
Zavvi has a right to ask for the product back - the problem here is using the "nuke" option instead of the "diplomacy" option. After all, instead of the letter threatening action, they could send an informative letter first - perhaps saying the item was shipped in error, and that the customer could buy it at a steep discount or return it with an enclosed shipping label - just stuff it back in the original shipping box, and paste the shipping label on top (heck, they make small packs of tape so you can seal the box without using your own tape!) and call the shipper to pick up the item. And sometimes even eating a small loss doesn't hurt as well - for using either option, since it was a $20 game, just refund that money as well. Those who don't send it back? Then pursue them legally - give the customer a chance to be honest and let them benefit more by doing the right thing - either by getting the item they ordered free and a discounted Vita, or free item and a returned Vita. Either way, you overcompensate the customer, they feel good, and are generally more than likely to do the right thing immediately. The company's already out the cost of shipping, and the RMA will cost them some more (what happens if the Vita was opened?).
Hell, even Logitech doesn't do RMA all the time - the costs (shipping, RMA manpower, etc) can easily outweigh the cost of the item, so they just ship out a brand new product as a replacement, or demand return of a small item of the original product - cheaper for them.