Large (transport) aircraft aren't required to be certified to the same standards as smaller (normal) aircraft. For some things, they have more stringent requirements (such as redundant systems), others they don't (such as spin testing). Part of it comes with the fact that these larger aircraft have much higher training requirements for flight crews.
If you're really interested, take a look at the various requirements by looking at FAR parts 23 and 25.
Part 23 covers the airworthiness and certification standards for Normal, Utility, Acrobatic, and Commuter category airplanes. Part 25 covers the requirements for Transport Category airplanes.