Hi, I'm not sure what are the terms from Best. The one from HN is actually in the form of insurance. Which means that if it fails 5 years down the road, they're still obliged to repair it for you. either that, or they can replace one of a similar value. So I can actually see this as a protection.
So you buy 10D at 3099 from HN, then add a couple of hundreds for the extended warranty. 5 years later, it fails, maybe you get to exchange a 1Ds Mk III or something similar
Regards,
JK