yes, when I was debugging kindle and google books with catlog, that's exactly what I saw, there was an unsupported UI call in each app that was causing the freezes/crashes.
the reason for changing the old version, even if it works, is the usual/obvious: one would imagine newer version has bug fixes, better performance, added features, etc.
what is not obvious, but more like puzzling, is why in google market/play, when they generally seem to do a good job matching app versions to device signature (sometimes a little too good... I'm sure we've all seen an app we know just works fine "disappear" from market) - why they would allow newer app versions with additional/incompatible API calls that are known to be unavailable on a given device/version, to be displayed as compatible for that device/version.
(although in this case, the very latest kindle app and google books app work just fine on my 2.2 phone - so it's more likely that Ermine is still not quite complete version of 2.2 even though it presents that signature)