Even when new they look all dusty and smeared, why is that?
You can just see the dust in the air get sucked to the lens.

What seems odd is that the dust doesn't seem to make a noticeable difference in the picture quality. After I clean my lens, I don't really notice any PQ improvement. I guess that is a good thing, otherwise I would have to clean the lens every time I used the projector.

P.S. I don't notice smears on my lens, mostly it's just dust.