Well, as far as uphill and downhill goes there are a lot of cultural differance to consider. While we do have some similar tastes, Japanese and Americans do have differant standards on a lot of things.
As far as how long Pokemon is going, consider that people are still recycling the whole "Amuro Ray: Gundam" thing... the very first stories, with some success, and that is even older than Pokemon.
I guess part of the thing is that a couple of cartoons have become defining parts of Japanese culture as a whole. Something that seems odd to a culture without anything similar. I guess you could consider Gundam and Pokemon sort of like the Japanese versions of "Gone With The Wind", "Citizen Kane", and "Casablanca"... viewed as equal works of cultural art there (even if they wouldn't use that term) and which will never die.. despite being series as opposed to stand alone works.
I know some people are probably going to roll their eyes at the thought of Pikachu being the "Scarlet O'Hara" or "Rhett Butler" of any culture's pop cutlture... but the phenomena sort of speaks for itself.
Such are my thoughts.
I'd half expect that if we ever sent forward the best media our cultures had produced those three enduring classics would be on the American short list, and Mobile Suit Gundam, and a couple of the Pokemon movies (if not the whole series) would be somewhere on the Japanese ones.