There was a thread on this I read earlier, I think people said it is because it only can be needed by the class that has optimal use for it, in other words yeah you can wear it but the tank would probably benefit more so you can only greed.
That's just what I gathered from the conversation, as a DPS you would probably wear it for a shorter time because you upgrade a lot for better damage stats and what not.

Not saying I agree with that, I think if it has LNC on it we should be allowed to need, but there you go..