Agreed. Depending on the search the #17 position might not appear until the third page. The vast majority of people don't get past the top three results and almost no one makes it to the bottom of page two or page three. You might get one extra visit a month moving from 40 to 17.
Also the penguin update doesn't specifically penalize new sites. It was primarily directed at sites with unnatural back link profiles.
I have had a similar experience with small businesses over the past year. Even if they don't know what WordPress is someone has told them that they should use WordPress.
I position any project as a way to increase business through design, SEO/SEM, conversion rate optimization, but I find frequently that WordPress is a selling point.