We're planning to drop support of Android below 2.1 in upcoming weeks. There is a very small number of devices that still have Android versions below 2.1, and supporting those means less features for everyone else. For example we can't do proper animations (including transitions) because they're not available on pre-2.0 Android. Even when we started developing for Android, we couldn't find a device with Android 1.5 to buy for testing. Take a look at latest stats:

http://developer.android.com/resources/dashboard/platform-versions.html

As of September 5, 2011, less than 2.8% of all Android users use version 2.0 or lower...