....
"except Naruto and DBZ"???!!
Boy you can't have read many mangas can you?
First of all, it is widely believed that '***' sells(looking at certain trends you'd notice that it is probably the case as well), thus the extensive use of it. Now it doesn't have to be intercourse, but might as well be mere nudity or mini-skirts as you've pointed out.
Now, apologize to all the hard working mangakas out there not using such meek tactics because they've actually got good story enough to not need it at all!
Also, just to defend some whom actually use it(you couldn't even say that); it's more about the intention and using of it that matters:
A girl falling down on top of a bed in full nude with an overly excited MC(please refer to trouble/to-love ru chapter 1) vs. a 'no-boobies, no-bottoms back view which is intended only to show that Riza has a tattoo relevant to the story' (please refer to chapter 57 of Fullmetal Alchemist) kind of situation.
It doesn't even compare to be honest, completely different dimensions and oh do I wish Kentaro stopped that stupid series and did something good like Black Cat again.. Haaa~
Whatever, what you want to do is to read 'to LOVE-ru'. I'm sure you'll love it and make sure the door to your room is closed and that you're home alone before getting too intimate with yourself, hence developing a situation between your computer and you. ;D