there is, j-pop is centered more on very young women. so much so that its almost impossible to get work as a j-pop star after turning sixteen. k-pop aims at a more adult audience and the talent reflects that. that being said, they do have very similar sounds, but i'd argue that american pop is just as similar.
No problem, I used to have a problem telling them apart. Only through listening to/watching lots of jrock and kpop did I learn to tell Koreans and Japanese people apart.