^ Yes and no.
When it comes to Pop-music, 99% of the songs are about "love", or just lovely relationhips. Maybe 75% of these would be about sex, even if it doesn't reaaly look that way.
These are invented numbers, I'm just guessing them by experience. And it's like the general average for the entire world. Japanese are unique so it variates a lot.
When it comes to idol music, almost all of it would be about love because it's what sells, and I guess they wouldn't make many "mature" (cough-cough) songs because it would generally contradict the image of the idols they're selling too. I mean, you can't just make these "pure" girls to sing about "the best night of their lives" or "the time they truly felt as women" (which is repeated like in 1 of each 3 American pop songs). But of course you can sell her if she's saying "I love you much, very much much much". Imo, at least.
So no surprise that a great part of H!P's songs would sing about love.
Anyway, i still think that, given the fact that H!P threats with teenage girls which are still at the age of being educated, and given the fact how actually Japan's society is, all the songwiters of H!P are doing a damn good job - they're really helping the girls keep growing, to say it so....