If the image is cached, then when you call up another page (or refresh the same page) that has that image on it, your browser is going to say "Hrmmm...'AnnoyingAd.gif'? I've got that in my cache, so no need to go out on the network and get it!" So multiple pages = one image download.

Pageviews and click-throughs are both counted. The latter is much more desired, but the reality is that it is still usually around 1% or less of the pageviews.