Sometimes ads don't make it past the concept stage. Sometimes ads are brilliant but the clients is too conservative to run with the idea. And sometimes they just run out of money.
Advetising and PR Communications people Sellers & Rogers have published 2 nice little booklets with some of their best ads that never made it to print. You can download them for free from their website. I personally think the Lionel Richie one above is sheer brilliance.