Both kie-api.jar and drools-compiler.jar contain org/kie/KieBase.class.
It looks like drools-compiler is fat jar. Fat jars (even shaded fat jars) are evil. See slide 39-42:
http://ge0ffrey.github.com/maven-dependency-puzzlers/maven-dependency-puzzlers-presentation/src/main/presentation/index.html#39.0

Certain platforms (android, ...) don't even allow to deploy such jars. Others (osgi, ...) throw warnings.