Gave this topic some thought and tried to understand why I prefer Korean rap/hip hop over Jpns as well as rest of Asias. Although i don't agree wholeheartedly that there is such a thing as a "hip-hop standard" that should be followed, there is not doubt certain elements/ styles/ sounds of rap music which makes it more "hip hop". This parallels that "real" vs. "fake" hip hop discussion not just in that the English/ American forms are seen as more "legit" as compared to outsider foreign "wanna-be/ fake" forms but also that mainstream hip pop vs the underground backpacker aspects of it as well.
To me Jpnese "hip hop," and this could be said for most of Asia as well has this "Asian pop" overtone to it which makes it just too Asian sounding as exemplified by all the Jpnese hip hop MVs from all the previous posts. Not that that is a bad thing per se but it does make it seem less "legit" compared to their American/ English counterparts. This is similar to what Kami stated above, but I don't see hip hop as solely a "lyric based genre" because if you are a big hip hop head you will instantly "know" when you hear great hip hop/ rap, a gut feeling if you may. What I am trying to say is that hip hop is not only defined by its "technical parts of their lyrics" but is also defined by its overall musicality which is derived from all the elements/ instruments that are used. Lyrics is just one component of that. Hence, even though I don't understand a single word when I listen to non-English hip hop I can still dig it due to its hip hop musicality.
I guess that is the basis for my Korean hip hop bias because for me it just sounds more "hip hop" and "legit" when compared to the rest of Asia. Sonically you can hear the "realness" in Korean hip hop, because there is direct correlation in the elements that are used to what we would now consider as that "Classic Hip Hop" sound. No doubt there is a lot of sh!tty Korean hip hop out there, but amount of talent that is harbored in Korean hip hop scene despite its small niche in Korean society is massive. Korean hip hop, where it lacks in quantity, is made up by quality. Sadly this could not be said for the rest of Asia because both quantity and quality are lacking. Despite the popularity of rap/ hip hop in Jpn, I find it extremely difficult to find quality artists that appeals to me. A lot of the successful acts such as M-Flo, Zeebra, AI, etc just can't compare to what Korean hip hop has to offer. That is why it was great to see many Jpnese hip hop MVs posted here, because for me it is extremely difficult to find good Jpnese hip hop with that real classic hip hop feel. Despite I loved all the Jpn MVs that were posted, it still has that Asian pop overtone which can sound generic and too poppy at times.