a little dose of perspective
To put things into perspective:
Hard landing is a landing over 10 fps, because civil transport aircraft are certified for limits loads produced by 10 fps landings. It takes about an 18-inch drop to get 10 fps, assuming zero lift (that's how high a landing gear drop test is).
Boeing and Airbus also define g's for identifying hard landings from FDR data. These levels are usually in the range of 1.75 to 2.2 g depending on aircraft type and weight, and are conservative to account for lower than ideal sampling rates of acceleration parameters.
I'm not saying that civil aircraft never drop 20 feet or 100 feet hard onto runways... but they usually leave a smoking hole when they do, because they're not designed for it... it all depends on how long it took to drop those 20 feet. 12g landings also have a tendancy to leave smoking holes and bits of aircraft lying around.
Hope this helps clarify.