I don't think that Big Eyes, Small Mouth (in anime), young girls having relationships with adult men (also in anime), and 13 to 17 year old pop stars can be construed as evidence of lolicon in Japan; I'm not saying that it isn't prevalent, to some degree, in Japan, just that these things aren't good evidence for it.

Most anime/manga characters (in my experience) have small mouths unless they're smiling, frowning, or talking loud. And while women tend to have larger eyes in anime than men, I'm under the impression that this is because "big eyes" = "cute" in the Japanese culture. Thus, I don't think Big Eyes, Small Mouth is any indication of lolicon.

And while there might be a lot of anime with adult men and younger girls, I don't think that much of this is catering to, or influenced by, any sort of lolicon. Most of the stories where this occurs is written by women for girls. Many of the girls who watch/read this anime/manga have fantasies about going out with older men, and many of the writers had such fantasies when they were girls themselves; it's a form of wish fulfillment. The only shounen (boys) series I can think of with lolicon element is Maze, where the barely-pubescent Mill is in love with college age Maze. However, she's in love with both male and female Maze (who switches genders depending on if it's day or night), male Maze goes after anything female old enough to have breasts (which Mill barely has), and... It's just so weird in the sex/romance/gender departments that I don't know if it should count.

Of course, in all anime/manga there's lots of unrequited crushes by girls on older/adult men, but I don't see that as having to do anything with lolicon; that's just life.

And the 13 to 17 year old girls who are Japanese pop stars... Considering the popularity of the likes of Britney Spears among young girls in the U.S., I wouldn't be surprised if their primary audience was young girls. While men with a lolicon would obviously be fans of these idol singers, I seriously doubt that they're the driving force behind the phenomenon.

Examples of shoujo (girl oriented) anime/manga which have loliconesque relationships (and not just crushes by a young girl on an adult man):
  • CardCaptor Sakura, the manga. 10 year old girl Rika gets engaged to her homeroom teacher, Mr. Terada. (That's right, engaged)
  • CLAMP Campus Detectives. 5th grader Takamura Suoh and 4th grader Iyuujn Akira each have an, err, "girlfriend" who is in kindergarten. Really.
  • In Magic Knight Rayearth, 14 year old Hikaru ends up with an adult man.
  • In Fushigi Yuugi, 15 year old Miaka gets a virtual harem of adult men who are interested in her, and she returns her love to one of them (Tamahome).
  • In Sailor Moon, 14 year old Usagi (Serena) and college age Mamoru (Darien) are a couple in the anime. (Mamoru is somewhere from 18 to 20 years old; it's never laid down exactly how old he is). In the manga, he's a high-school senior.