I think part of the reason why Kpop has been getting the big boom lately is because some anime/jpop fans got curious because of the somewhat rise in kpop popularity. I'll admit, I would have never listened to BoA, Se7en, or Bi (ugh I can't believe I admitted that...) if it weren't for Morning Musume (who i listened to because of anime). So I think those who followed and stayed tune to the jpop scene (especially around 05/06/07) noticed that there were a lot of Koreans (other than BoA) that were getting big in the Jpop music industry, thus leading their curiosity back to where these Koreans came from and what style they had before. I think it got even bigger when DBSK (and SS501) brought some of their kpop style and mixed it with Jpop during the rising popularity of boy bands (or come back of boy bands) in Japan. Again, LSM is just genius. But we can't forget that Kpop was once an underground music genre in Japan at once point. Only a few groups (bboys for example) listened to Kpop because of their beats and rapping, which if you compare to J-urban sound so different.
But I don't think all of this K-entertainment popularity happened because of music. Even Korean actors/actresses are getting big in Japan through their dramas (well mostly dramas). I know a good amount of K-actors have fanclubs already.
And a way to tie SNSD in here

: I find it a bit
odd ironic funny (?) that SNSD is striking popularity in Japan. I thought Japan grew over the whole "big girl groups" stage after Morning Musume and other H!P groups. A few years ago, if SNSD debuted back then, I would have expected more exposure to Japan (especially since LSM loves Japan). But now, I didn't even think they'd be talked about, much less mentioned by their "opposition", Morning Musume.
-O_sLaVe