The optional interim services apply fo as long as your driving in conditions that necessetate interim servicing. Like Adamsy said, bumper to bumper traffic, extreme temperature conditions, regular thrashings, etc. They're still optional, and therefore not doing them won't effect your warranty. Once you're out of your new car warranty and into your extended warranty, the "compulsory" (for want of a better word) intervals in your service book go out the window in favour of the intervals as stated in your warranty policy. So the fact Aurion has ordinary 15,000 and optional 7,500 intervals, even if your extended warranty agreement says you get your car serviced once a week or every 500kms, thats when you do it if you want to keep your warranty valid.