Yea, I see that too to some extent.
I often read a lot of threads but don't comment on them. I probably post on half the threads I read at most. Often times someone else has already said what I was thinking so I move on without posting. I don't say to myself "theirs a thread by so-and-so, I don't want to bother posting there, oh and here is a thread by my friend, I think I'll post there." I read and then post where I have something to say.