For a small forum community, it might make sense if the forum owner or admin responded back to every new discussion created. That would be especially true if there were only five or ten very active members on the forum daily. But, when there are dozens of members posting daily, is it really necessary for the forum owner or admin (whoever is running the forum daily) to respond to every new forum discussion created?
No. What if something is being discussed you have no knowledge or interest in, such as a movie or band or video-game? Just because you're the board owner or an admin doesn't mean you should force yourself to falsify interest in things you clearly have no real involvement with. Even for a smaller forum, I don't think it matters for an admin to reply to every topic. Missing a few out here and there isn't going to matter much if you're still addressing the majority of topics.
If you have a really active forum then no, definitely not, but a small community just getting started, you need as much activity as you can so replying to every thread is a plus in my opinion. It also shows that the admin has a strong presence there and is always active.