I do not remember being asked during the interview about what other programs I was applying to. One student that showed us the campus asked, though.
At any rate, I would bet that only a very traditional/old-school program might care that you only apply to DO schools. Of course, we all only want people that wish to be DO's to actually get in to our schools. However, I applied to both because more than wanting to be a DO, I want to be a damn good doctor. Aside from that, I also want to attend (and give $$$$ to) a school that I feel very comfortable with (meaning location, faculty and staff, students, resources).
Another thing to consider, it is a good idea to apply to as many schools as you are willing to attend, but don't go crazy. You will likely be a fine candidate. Remember, if you mark 15 or 20 schools to send your primary ap to, then you will likely have 15-20 secondaries to complete right at the same time. I know you are motivated, but you may also be busy trying to make enough money to pay for this costly endeavor. Also, by the time you are on ap #12, you are probably getting sick of spilling your guts in a matter that is gramatically correct packed with beautiful verbage.
Let's just say you applied to 20 schools and recieved 5 interview invites. Since you are highly motivated and applied early and jumped on the secondaries without delay, all of your calls to interview came within a two week period. Unfortunately, they are all over the country an none are within driving distance. Since you are eager to shine and know your chances are much higher with an early interview, you jet set all over the place. It pays off, you recieved at least 2-3 acceptance letters/calls and now struggle with deciding between you top two choices. You will pay it back later in your career, but you didn't realize that all of this credit card debt before starting school looks bad on your credit report that is required to get all of those education loans.
My suggestion: Research as much as you can about the schools. Choose your dream schools and your back up schools. Don't let averages of incoming students scare you away from the dream schools, but don't forget to keep it in the ball park with the back-ups.
Good luck.