Yes the super human abilities are fairly strange but there are a lot of super human abilities that occasionally show up in real life some as seemingly unrealistic as what is shown in Ranma. Ex. mothers lifting cars to save their child, people falling off high places and not being injured, car crashes where the car is totaled but the driver walks away without a scratch, men pulling trucks, remote viewing/astral projection (military and government agencies believe in it enough to spend millions of dollars on it), etc...
There are real life items and things that are some what like the magical items shown in the manga. Ex. anti-sleep drug that allows you to stay up safely for almost two days while remaining practically as focused, alert, and capable of dealing with complex problems as the well-rested. http://www.boingboing.net/2002/06/27/ne ... _drug.html another ex. invisibility cloak - Japanese built one of these, another ex. drugs that increase suggestibility and drugs that erase short term memory.
Actually some of the supposed weird things in Ranma aren't all that weird. There really are martial art schools that teach both martial arts and ballroom dancing so it's not a big stretch to combine them.
Martial arts tea ceremony has never existed as far as I know but several schools of martial arts do suggest that their students learn tea ceremony and flower arranging as a means of learning patience, control, and other stuff. Also like martial arts it usually takes years to become a master at tea ceremony.
Both Rhythmic gymnastics (similar to some Chinese martial art styles) and cheerleading (some places teach both so why not combine them) can be counted as martial art forms.
Almost every high-school in Japan does have martial art clubs and competitions involving martial arts.
Watermelon bashing races exist they just aren't like in the manga. Blind fold and hit with sticks whoever breaks the most melons in a set time period wins and eating contests.
There are whole communities revolving around martial arts.
There are also little known tribes in existence today for example the many small tribes in the amazon rain-forest.
The amazons laws aren't all that weird just way out dated. There are plenty of real world laws that brutal and a ton of much stranger laws.
ex.
-In 100 A.D., the Teutons, an Germanic tribe, would punish anyone caught as a prostitute by suffocating them in excrement.
-The vow of a Roman vestal virgin lasted 30 years. If she engaged in sex before then, she was punished by being buried alive.
Oh and I have no idea as to why I wrote this but it probably came about from seeing an artical about a woman lifting a car in the newspaper, discovery channel showing something about remote viewing, reading about weird laws on the internet, hearing about the no sleep drug on the radio, and other things I recently saw that make it seem like the real world and Ranma world aren't all that far apart.