lol I love that site. One of my personal favorites is the one on the Katana, and how it's cutting power is GROSSLY exaggerated.
On the subject of martial arts stereotypes, my favorite would have to be
The Law of Conservation of Ninjutsu.
Looking up the katana article lead me to the Tropes list of Japanese sword-types. It was more succinct than the Wikipedia equivalent.
Indeed. I also like the one, All Japanese swords are Katana's trope as well. For fun, tell a Japanophile that Japan once used double edged straight bladed Jian style swords and Chinese styled armor. They will blow a gasket.