I have that feeling as well but I also have a perfectly good explanation for it based on my own example. When I am opening a thread that post usually takes much more time and effort from me than a reply on someone else topic which results in longer and hopefully more valuable post to the community as whole. Or in other case I am running a gambling pool or something and OP is like the default place for people to recognize my efforts throughout the entire thread which lasts for whole year or even longer.