I don't listen to J-Pop.
American popstars usually go like this:
1) They make a debut video. These girls are usually 15-17. Some, like Mandy Moore, were even younger. These lolitas are designed specifically to appeal to the male audience. Insecure females, seeing the attention these girls get, rush to either buy their albums or imitate them.
2) They are featured in a risque photoshoot with Rolling Stone, Maxim, FHM, etc. In this issue, they discuss how they love porn, masturbate all the time, and talk about their intelligence. So that way, on FHM's cover, it can say, "<Popstar>, Hot and Brainy!" I'm sure many of these popstars endorse the hot but brainy act because even though they got their attention through looks, they still want to believe its because of their overabundance of talent.
3) The popstars put out a new album, which shows their depth and growth over the past year to 18 months. The album here typically tends to do ok but not up to the high standards of their previous album. These popstars may also "branch out" by having some tracks produced by the Neptunes or Timbaland. Some collaborations are also featured. In short, the popstars try to act deep to get some long standing footing. What happens when your popularity is based on your T&A?
4) The breakdown. The popstar then either becomes promiscuous, drinks like a fish, takes drugs, or some combination of the three. These girls now are clinging desperately to their fame. Some of them may try crash anorexia diets. Anything to drum up high levels of publicity. Any publicity is good publicity. Meanwhile, their record label drops them, usually around the second or third public embarrassment.
5) Their recovery. By going on every talk show that is willing to host them and giving any interviews possible, the popstars then talk about how they overcame their struggles. How now they are finally happy.
6) Their failed subsequent albums. The popstars then put out a bunch of albums that are lucky to even get Gold. Expect to see them take either one of four routes: Playboy, fading into obscurity, being featured on VH1's Surreal Life (or some other VH1 program), and continuing to put out albums that make desperate attempts to rekindle sales that matched their debut album.