Why aren't iPod Touch users upgrading?

I use the analytics package from Pinch Media with my apps. One of the interesting things that I get to see with it is the breakdown of what OS version my users are using. I also get to see what percentage of my users are running an iPod Touch vs an iPhone. Now what I do not get to see unfortunately is the breakdown of OS usage by device type. That would be very interesting indeed. What really piques my curiosity is that the percentage of my users that are running iPhones (70%) and the percentage of my users that are running OS 3.0 (72%) is intriguingly close to the same number.

But, as my Pragmatic Marketing friends are fond of saying, "Your opinion, while interesting, is irrelevant."

So I've done a little poking around on the web. Admob published some interesting numbers the other day that claim that only 1% of iPod Touch users are upgrading. Admob published those number June 22, 2009. So here we are a few weeks later and I suspect that the numbers are a bit different. But as an iDevice developer, I still find that number disturbing.

So, why aren't they upgrading? Performance statistics like these from PCmag can't help. Is it the $10 upgrade price? Are there just not enough compelling new features in the new OS?