Why are you doing oil changes every few months? Use synthetic and change it every 12k miles.
$600/year is outrageous and more than I've ever spent on maintenance before (granted I've never owned a car that cost more than $50k) and EV's are supposed to be "simple" and "low maintenance". I agree with qwk that after first wave of nutters (that would be us) people are going to balk. Especially since they're comparing Model S to a 5-series where all the maint. is free for the first few years. They're going to have no choice but to follow the germans down this path.
My Ranger mentioned a while back that most Model S maintenance will be done remotely through 3G, so he expected the actual physical work required would be minimal, and therefore the cost would be lower.