From a chef's point of view, the most significant difference between a Japanese knife and a Western knife is that nearly all Western knives are sharpened on both edges of the blade, whereas many traditional Japanese blades are sharpened on only one edge. This style is called "kataba" (片刃　）.

http://www.toyokuni.net/mente/dumen.htm

Most "kataba" blades are right-handed. So if you're shopping for a left-handed cook you need to ask for a special one with the left edge sharpened instead. (If you're interested, you can start another thread to discuss Japanese attitudes towards left-handedness).

Having only one edge of the knife sharpened allows for cleaner cuts and more precision, but learning to use only one edge requires practice. Needless to say, many Japanese people have opted for two-sided "ryouba" (両刃　） knives for home-use.

There are other differences between Japanese blades and Western blades - in the types of steel and techniques used to build the blade. But I imagine that from a chef's point of view, these are not obstacles to using the knife.

I think the comments about Japanese intestines being longer (and no word for "no") are intended as examples of the bull$hit that Japanese trade negotiators have used to explain why Western products should not be admitted to these "unique and special" islands. "We can't allow your pharmaceuticals to be sold in Japan, because of the uniqueness of the Japanese digestive tract." etc.

In the case of Japanese knives, it is no bull$hit to say that Japanese blades are different.

ADDING LINK TO WIKIPEDIA. This tells you more than I can:
http://en.wikipedia.org/wiki/Japanese_kitchen_knives