If an author puts out bad content, long or short, people will be less likely to read his/ her future content. It's like with anything else, if you like it then you're willing to spend more time with it (on it). Additionally, a feature that allows you to "take back your voting time" would remove any rewards given to the author based on their lengthy article.

Also, it might also encourage posters to cover their topics more thoroughly, making for more valuable content.