I have been guilty of uploading screenshots as attachments which makes them hidden until you reply to the message. The way around that, which Frogz pointed out to me, is to host the screenshot on an image hosting website (I use photobucket) and then insert the photos into your post so ONLY the attachment of the theme is hidden to the reader until they reply with a simple thank you.
What I find completely unacceptable is the people who upload themes and provide no screenshot whatsoever. Who would download a theme without knowing what it looked like first?