dmax, when some people constantly encounter a certain class of comments over time, it becomes quite difficult for some to differentiate between the hackneyed comments from a more original one.
So when you bring up Yang and CMC in the same post, it is very hard for a seasoned mind to tell the difference between a comment claiming CMC is Yang from your comment about people changing Chen to Yang and Yang to CMC. I'm having a hard time too, but I can just about see the different angle you are coming from.
I've experienced having my comments brushed aside because people didn't take long enough to look at what I'm really saying instead of what it looked like I was saying. Just recently, I was accused of trying to talk about what I don't konw of Taiji, when I was really talking about people making judgements about one thing using a completely unrelated "clues". You've probably experienced having your comments mistaken before this. I'm sure Xue Sheng has as well.
The only way to get around this is to understand that the internet is the best place to encounter repeated arguments as if the people that made them thought it was something new that no one has thought of before. And you must understand that the people who encounter these hackeneyed arguments develop a set of conditioned responses. As time goes on, the conditioned responses seem adequate to answer related arguments as well and so they become used beyond their context. However, it's also hard not to see when these conditioned responses do not apply. You try not to bring attention to this because that will drown out your own point. Instead, continue to reword your thoughts to help them understand. Or quit. Either way is fine. It's not anyone's fault.
So to answer your question, I don't think Xue Sheng thinks it's an important point such that it must be brought up in every post with the words Yang and CMC in it. It's more of a conditioned response, I'm guessing.