I'm aiming to write an application for galaxy tab and decide to use platform 2.2 for coding . I don't know much about the differences between platforms but the tutorial that I use to write the app is using 2.2 so ...
now I want to know if it's a good choice ? could I optimize the app for platform 4.0 later on ? The app has some 3D animation parts too . could it be run in other android phone ?
If you do not miss any functions that are not available on 2.2 you will be just fine. The lower you are programming without missing anything the more devices your app can cover. Later you can still go higher with your programming, but a low start can be good. But be aware that the sourcecode in V 4.0 is open source, so your learning experience could be more easy ;)
On the galaxy Tab you have 3.1 as far as I know, so there are a little different concepts possible, but not necessary.
Here is a comparison
http://socialcompare.com/en/comparison/android-versions-comparison
Hope this helped you a little