I see what you're saying but, I think message boards attract a certain "type" of individual more so than others. A lot of people have downtime and don't read message boards during it. They can also be doing other things while doing any one of those things you mentioned: video games, watching movies, groupies, clowning with their friends/entourage, etc. There's also FOMO so a lot of folks on forums like to think the ones they visit often are more important than they may realistically be. If they do happen to scope one out, it'd most likely be something on reddit, probably like the reddit front page where pictures can be posted and they get a major news stream. This forum in particular, do you think they like seeing a forum that is 1/4-1/2 race threads or that gets most of their thread topics from social media anyway?
My girlfriend is a music journalist and I've actually met a few record producers, songwriters, etc. through her or her co-workers. One of my best friends is a doctor who has famous clientele here in Los Angeles, another one of my best friends is first cousins with another artist/producer who has made top 10 hits (as in pop charts) within the last year. I've had plenty of chances to interact with these folks, even at house parties in the nice Los Angeles areas when they are being very casual. I asked some of them straight up about message boards, even just under anonymity - some of them didn't even "know" stuff like this exists, some looked at me like I was weird for going to them, others thought they were lame. Not one mentioned anything about posting/lurking on them.
My theory is that when you get that famous, you stop caring what tabloids say about you and thus stop caring what the general public are saying about you. Plus many have to some of the best mental health professionals (power of money and fame) there are when they need to talk.
Even look at their comments on social media, even on "fake" accounts they've made when leaving reviews: most of the time they're very abrupt with an emoticon.
What it really comes down to: some people like to do more than they talk and some that like to talk more than they do. A lot of the former may seem to be more "superficial" than the latter. But I do think famous journalists or people who write for magazines are more prone to visit these sites.
