If there's a software update, new demo, or some other kind of news that's important for LightWave people to know, it's OK to mention it there, since some messiah/LW users don't frequent this list and messiah is (amongst other things) a plug-in for LightWave.
I guess if someone there posts a messiah question and it doesn't get moved here, it's OK to answer there. The thread might get moved here, and it might not. For example, if the question is about someone having a problem using messiah and LW together, that might be a LightWave forum question (though not all the time). The analogy I can think of is that if someone has a question about using Photoshop for their LW texture that would go on the LW list, not on the Photoshop list. But a Photoshop question like "how do you make custom brushes" would (or should) go on the Photoshop list even if the person using it for a LightWave texture.
Here's a messiah/LW example: If someone on the LW list asks about some kind of character setup and wants to know if there are any plug-ins that might help solve some of his problems, it's fine to post a reply there.
Ultimately, if a thread does get moved from there to here we'll look at it on a case by case basis. None of the other lists for messiah host apps have had any problems or complaints, so I think the LW list will calm down too, as long as we (or _I_) keep cool.