Of the Android devices that have access the Google Play store in the last 14 days, Google reports that 10% are running Froyo and another 4% are running a version older than Froyo. However, I imagine the number of Froyo devices is even higher if you include crappy devices that do not use Google's Play store.
More telling to me is a browse through the smartphone section in big Tokyo electronics store.
There are probably on the order of 30-40 different models, and I'd say at least half say "OS: Android 2.0"... :(
[Those are typically older models, of course, but with new phone models released constantly, the oldest are not more than about 1 - 1.5 years old. Also, some of the models I saw running 2.0 looked pretty up-to-date hardware-wise. It seems manufacturers are not always so keen to use the newest OS version...]
You need 768MB of RAM for Android 4, and realistically a decent GPU. 256MB and the most basic $0.50 ARM chipset from Qualcomm [1][2] will get you up and running on Android 2.x.
Yes, it is a bit, but not like iOS6 would run much better on these devices anyway. If the new chips can use some decent GPU's the experience should be significantly better on ICS/JB than on Froyo, though, because the UI wouldn't use so much CPU time anymore, and wouldn't choke as much doing regular operations.
No amount of efficiency in a new version will instantly get all the old devices upgraded. Froyo will live as long as most devices it came preinstalled on.
From the specs:
> Android OS, v2.2 (Froyo)
It just won't die...