I don't think there's anyway that it can be a sustainable trend. You'd have to have one hell of a product to get a positive ROI on that CPM (plus you have to add in Apple's take).
I imagine it's a lot of novelty of the platform, and the fact that iAd is a good bit more engaging than most of the other ad platforms. Eventually ad fatigue will set in though.
It's a huge rate, that's for sure. I'm sure it's due to the reasons you mentioned- these ads will remain viable for some time. The actual rate paid out is likely not sustainable, though. Same thing happened to AdSense when it launched- those who got into the private beta in April/May/June were doing gangbusters until the market settled down after that summer.
