I would have two or three specific reasons at the ready in case the interviewer IS former military. Even if they are not however, it's not a bad idea to have some specifics ready - it'll make you more human.
For example, if, while you've been in, you've gotten married, had kids, 9/11 happened, and your folks aren't getting any younger and will soon require your assistance, stating all these as concrete reasons for your decision will demonstrate your dedication to family. No one questions your dedication to your country - that goes without saying. What you will put on display something they might indeed be interested in.
Think creatively about what you want a company to know about you - work out your strongest selling points - the reasons why an employer SHOULD want someone like you on staff. If you do this correctly some of those things will be in the realm of maturity, reliability, family orientation and adherence to duties related to all of these.
An interview is an opportunity to take complete control over the flow of information that another person will hear about you. Make sure you’re ready to deliver the very best sales pitch you can. It makes all the difference in the world when you come prepared.
TIS