Bill Sweetman's A-10 book gave me a real soft spot for the aircraft. As with all this series, he gave a detailed account of the design philosophy.
The designers were given, if I recall correctly, a maximum price of $80 per Lb for the airframe. If it couldn't be met, they had to use a cheaper material or process.
As others have mentioned, the A10 was designed to continue flying with a tailplane half, engine and outer wing panel all shot away.