Actually I do this for a couple of reasons. Regular dino oil I've read doesn't have a long shelf life in an engine once it's been used. Acids build in the oil and can cause excessive wear on engine components. They also don't offer the additive packages that synthetics offer. Seeing as I don't drive frequently and change oil twice/year I find the benefits worth it.
The other reason I use synthetic is a synthetic will maintain it's viscosity and lubricity at much higher engine temperatures, which the 500 can definitely see. If I were driving the car more often I'd change it every 3500 miles.
Great place to learn more about oil...... www.bobistheoilguy.com
IMHO I'd much rather play it safe and spend $60/year more for oil and not take any chances with my engine.