Your priority is to become a physician... whether your first choice is DO or MD, you want to keep your options open. I want to apply to DO schools because I like it's philosophy of medicine, but I'm also certainly going to apply to MD schools in my state.
ATPase is right. There's no need to tell them unless you want to (they have no way of finding out unless you tell them). Even if you did tell them, I doubt that they would care.
I don't know about anyone else, but at 2 of my interviews I was asked about the other schools. One of the schools actually asked me... "So how does your experiance during this interview day compare to your other interviews?"
Huh? Why would there be anything to justify? If any school expects that you're only going to apply there, and no where else, then they're absolutely unreasonable, and you should tell them that.