Human choice is really complex. Having said that, I am not sure if your assertion is really correct. If you are very hungry in a place where all the restaurants are empty, I believe that you are going to choose one by yourself. Maybe what your marketing book is trying to say is something based on the so-called herding behaviour. If there are two restaurants and one of them is full of people and the other one is empty and you have no previous information about both restaurants (and your are not considering other factors such as waiting time), you will probably choose the one that is full of people.
So, I don't think that adding one to every post will help people do anything. In fact, if every post has an upvote, this upvote will not help them to choose the best posts and people also wil not receive an upvote as something special, since everyone has an upvote.
If you want to motivate people to upvote, you may try to create a community, where the culture is to upvote good posters. I am not sure how to do that, but certainly is not to upvote every post... However, usually people follow some social norms such as reciprocity (http://en.wikipedia.org/wiki/Reciprocity_%28evolution%29) and if they receive upvotes for good posts (you may try that as the super admin), maybe they try to return the same kind of altruism. On the other hand, in this kind of site (usually) upvote is the only way to pay for a good job. Social norms usually go in this direction, if people realize that voting is a way to pay for the job.
I am not sure if I helped.