Although less accurate than other machine guns, the AK-47 is easier to use and more durable. “It's simple, it's cheap, it's indestructible,” Mr. Kahaner said. “You can fix it with a coat hanger and a piece of gum. You can bury it for 10 years in the sand, pick it up out of the ground and it still works.”
You mean it keeps working forever?! How are we supposed to make money out of something like that?
Seriously http://en.wikipedia.org/wiki/AK-47 has many interesting insights into the design and manufacturing history - given that it's basically a hybrid of the best bits of other guns, much of this information is transferable to other domains.