I would say that tenkara is perhaps a bit more broadly and loosely defined in America than has been conceived of in Japan. It is for Americans fixed line fly fishing. Japan has a greater focus on mountain stream fly-fishing than here in America. Here a certain contingent would just as well fish for still/warm-water species as for trout.
Yet in Japan, as well as here in America, the tradition of tenkara has come to be seen as coming from the commercial fisherman of the mountainous inland. Tradition is fine to acknowledge and even revere; but fishermen more often than not are going to extend a method to a (personal) logical conclusion. Fixed line fly fishing may likely go anywhere fishing with a fly-rod & reel may go, depending only upon the limitations of the fixed-line rod and a person's desire or willingness (do you really want to fish with a 15 oz. 28 foot $900 keiryu rod for 20+ lb steelhead? Perhaps not, but I've seen it successfully done in a Shimano video).
I like what one Japanese fisherman wrote about tenkara. Tenkara rods did not make tenkara. Tenkara made tenkara rods. Lighter keiryu rods, and to a lesser extent seiryu rods, are used as well by modern-day Japanese fishermen in the tenkara method. So what is tenkara in America? Mostly likely whatever any one person chooses to make of the sport for themself.
I agree with all the statements made above. With respect to the different rod choices now available in the US., I believe Chris's following little essay really hits the nail on the head: http://www.tenkarabum.com/its-all-ab...e-fishing.html
While the variety of terrain and fishing waters available in Japan is much more limited compared to what we have available here to us in the US, the fishing tackle the Japanese fishermen use is a lot more detailed and dedicated to specific targeted fish species and water types than we American anglers commonly use, and it is much more complicated than the view of Tenkara fly fishing we have been presented with from the major promotor of the sport in this country. And I also believe American Tenkara anglers should make Tenkara fly fishing what ever they want it to be to match their fishing conditions, fishing waters (be they warm stillwaters or slow warm water streams and rivers, or cold water lakes and streams and rivers), and all the various fish species found in this country. Make Tenkara fly fishing what ever you want and need it to be for your own enjoyment. Let the Japanese maintain their traditions and let us expand and develop our own set of American Tenkara traditions. But if people here want to import and maintaine the Japanese traditions of Tenkara fly fishing in this country, that's their choice and a perfectly valid choice as well. Its your fishing, do it your way but do not maintaine that your way is the only "right way to Tenkara fish".