I probably never would have noticed. Yep, mine has a gap, about the width of a piece of paper, all the way round. It's so uniform, that I assume it's designed to be that way.
(Tillsbury, are you holding the paper perpendicular to the screen, pushing backwards through the screen? That's how I slide the paper in... if I have the paper parallel to the screen, and slide outwards, it won't slide in to any gap)
Assuming that's just the way it is, then another way to clean any dust out would be a piece of paper! (Although presumably whatever cloth you wipe your screen with would be fine too) I haven't noticed it collecting dust unduly.