I don't know much about DRY belly landings, but I had the same question as Herb, so I did a little research and found a link (below) that suggests that controlled belly landings are extremely safe. Yes, you'll do damage to the aircraft but it can be repaired, while I assume the ditching in salt water results in either a complete loss of the aircraft or a much more costly repair.
Here are quotes:
"Gear-up landings are not physically traumatic events. They rattle the mind more than the body. You can take some comfort in knowing that you're more likely to sustain a bruised ego than a bruised body from what is taking place.
Bodily risk in these situations results mostly from fire, and for several reasons the odds are pretty good that there isn't going to be a fire. Considering that low wing airplanes have considerable dihedral, you're not even close to contacting a wing sump drain with the ground (high wing airplanes, of course, have an even greater advantage here).
The chance of a post-crash fire after a gear-up landing in these instances is so rare that I couldn't find a single occurrence as I searched the NTSB database for the last 10 years. I received 271 reports, and there wasn't a single fatality resulting from a typical gear-up landing. In the majority of these cases, both pilot and passengers weren't even injured."
These quotes come from the following AOPA's Flight Training web page, on whether grass or concrete is better for a belly landing (concrete is better):
http://flighttraining.aopa.org/magaz..._or_Grass.html
That same web page looked at another study of 329 belly landings, and there wasn't a single fatality from a controlled gear-up landing. (There was one fatality on the
SECOND belly landing of a Baron twin after an attempted gear-up take-off; the pilot forgot to put the gear down, attempted a take-off when the props touched the ground, one engine then failed,
and an assortment of untamed aerodynamic forces drove the airplane into the ground.)
Ernie Martin