Questions serve as an opportunity to "fill in" the employer on areas they may have forgotten to ask you. If they are not 100% that you can do your job (or are teachable) and that you will fit in with the company, it is your job to ask the questions that eventually give them certainty.
Shameless plug: Just released a book on informational interviews with a huge list of questions and walkthroughs on how to do them. Best way to get a job!
http://www.amazon.com/Informational-Interviews-Coffee-Superc...