I think it's really just common sense. For all its coolness, the AK-47 doesn't seem to me to be designed around historical sword specs - it's a large, thick, 47 cm long knife. It isn't as... specialized, I guess. Swords that I have seen run the gamut from wide, long and floppy to short, narrow and stiff. In the context of such specialized forms, it just doesn't make sense for a manufacturer to cover any and all damages when the sword, by design, is so prone to damage when used outside of its scope.
To expand a bit - swords that are meant to be nothing but swords have characteristics which make them poor performers outside their duties of cutting, chopping, cleaving or stabbing people. If you were to thrust the best made, thrust-optimized medieval type sword you could find into a stop sign, you would probably break the tip. Not because of any defects, but simply because the sword wasn't made to do that. An all-around warranty on a blade is great when it's offered, but it just doesn't make sense to do that when that blade is designed around highly specific tasks. The AK-47 looks like it would perform wonderfully at just about any task requiring a blade that long. Swords, however, do poorly when used for anything other than killing or maiming people.
To sum it up, if a manufacturer of fine tableware offered a Busse-style warranty, that'd be really cool. But I wouldn't hold anything against them if they decided that using a silver coffee-stirring spoon to mix concrete fell outside whatever guarantees they offered. There are swords that can handle a lot of abuse, but in my opinion, it's really asking too much to expect a warranty that ignores limitations in the design of a product.
Too long a post?