Almost every niche website I look at still relies very heavily on handles. Harry Potter fanfiction (and fandom in general) uses handles much more than real names. So do gymnastics message boards. So do sci-fi/fantasy book message boards. So does NaNoWriMo. So does gaming, obviously.
I think what you're observing is that as people grow up and become more "successful", a larger proportion of their social contacts become professional contacts. There's a very strong tendency in professional spheres to use your real name, because that's what you do business under. A large portion of America, however, works at the mall, or Starbucks, or WalMart, or other random McJobs where you can't really build a career. For them, using their real name gains them essentially no benefit but can easily cost them their job.
I think what you're observing is that as people grow up and become more "successful", a larger proportion of their social contacts become professional contacts. There's a very strong tendency in professional spheres to use your real name, because that's what you do business under. A large portion of America, however, works at the mall, or Starbucks, or WalMart, or other random McJobs where you can't really build a career. For them, using their real name gains them essentially no benefit but can easily cost them their job.