An ad is a virtual salesperson. Successful salespeople take the time to explain features and benefits, and to ask for the sale. They NEVER utter a few quick bullets and then walk away.
It IS true that no one reads irrelevant fluff. Nor will anyone pore over 500 words of copy before buying, say, a Bic pen. But people who are thinking about spending a large amount on a product they care about will gladly devour useful information.