Personally, I think it's true. For the simple fact that the vast majority of people are pretty boring to other people for one reason or another. And that the common person feels compelled to help or advise, for no ill purpose, despite often being unequipped to do so.

When you create a niche community, for that moment in time people are interesting to each other in the sense of having something in common, exciting even. As less serious folks inevitably filter in by word of mouth, linking, or curiosity, the SNR drops pretty considerably.

At one point in life I was a truck enthusiast and mechanical expert and joined a pretty nice community around it. It didn't take long for the laypeople to join, start sharing typical urban myths and terrible advice, and getting -upvoted- for doing so by other newcomers. It went from a community of highly technical folks to a community of commons, and lost all interest.

I'm no different. This was a Silicon Valley, startup, VC based forum initially. I found the community really interesting and loved the topics discussed. But I'm just some weirdo in the desert mainly sharing anecdotes anymore. That's not to say I exist to annoy anyone, but I could see some of the original folks being annoyed by people like me.