I did some research after our recent discussion on Kobe beef. The Japanese wagyu is indeed type of cattle, but it is the name given to three breeds of cattle that are raised in Japan. Then, there is Kokusan beef, which is beef raised in Japan. Kokusan wagyu then is the beef from wagyu cattle raised in Japan.
Do I think it tastes different?
Yes. But I think the difference in taste is more in the manner in which the beef is prepared than on the quality of the beef itself - or the combination of beef raised to be cooked in a certain way. Seared over charcoal in a wire basket, dripping with juicy goodness, sizzling every so slightly, this beef I had at Kase in Nagoya, Japan, was divine. The tender sweetness of the beef, without a trace of fleshy blood, tasted almost like the richest toro as the beef heated and the fat melted. A dipping sauce, made of various fruits ground up with soy sauce and other seasonings, was provided to add a refreshing dimension.
Would any old beef work for this type of preparation? Definitely not.
Do I think it has to be beef born and raised in Japan? No.
But the cuisine has to match the ingredients. This beef was raised to be eaten like this. It would not go well cooked in butter - prepared like that, it would never match the hanger steak I had in Paris. Local ingredients prepared to maximize its potential - to me, that is the height of culinary arts.