Is Android 2.0 backward compatible

I have a CLIQ 1.5 and a Droid 2.0 each wired to my PC via USB. I have written an application that simply reads contacts from the device (not some linked account) and they show up fine on the CLIQ but an empty list appears on the Droid. Don't tell me I need two versions of this app??? My manifest is targeti开发者_Go百科ng the least common denominator 1.5

Here's a blog posting describing how to make Android applications that target multiple OS versions and here is the official docs on versioning your application.