Hmm, I don't think that it's so difficult to "get" it. At least, many people use PP and view entities and we've never heard that anyone had problems with them.

But I'll do my best to make this issue more clear in the manual. You only need to understand one simple thing: view entities are totally unaffected by PP effects. They are rendered after all the views. Thus they just look plain on the screen. You can not use them for a view material simply because they are not yet rendered at the time when the views are processed.

If you want PP effects for a weapon, the obvious solution is to use a normal level entity and move it with the camera. It's just the same when you want other level effects like dynamic lights, fog, etc for your weapon - all this is not available for view entities. I think this is just sort of logical.