required to have your car serviced at the dealer. Of
course, if you'd like free warranty service, no other place will be
willing to give you that.
Like Brian said, anyone can change your oil. Furthermore, you're only
to do it every 7500 miles, unless you fall into their severe
usage category. I think this interval is too long, though. My opinion is
you'd be better off if you did it every 3k. But again, you can do that
yourself, or any facility of your choosing can do it for you.
If your dealer has told you that you must use their services to keep your
warranty intact, they are lying-- look for another dealer close by.