Many Android users would likely upgrade to Android 2.1 given the chance, so if we see Android 2.1 getting approved for devices like the HTC Hero, we should see 2.1 figures jump up significantly. As for how accurately this data represents the Android user community, Phandroid had this to say:
Again, I stress this data doesn’t account for every device, but it’s a pretty accurate representation considering the frequency at which you would expect the average user to access the Market (updates, looking for new apps, support, and so on).
With all the rumors of Android 2.1 update running around, we hopefully will see more devices updated to Android 2.1 by the next time data gets released on the topic. Interestingly though, with the rumors of Android 2.2 coming this year, we will see those numbers again split into four groups again.
Image from AndroidandMe