ASF source releases aren't supposed to have any jars within the release. However, the gradlew wrapper explicitly requires the jar to be checked in. To bootstrap a gradle build that doesn't have the jar requires the user to have gradle itself already installed, which defeats the purpose of the gradlew script.
I'm going to bring this up on the incubator list, since there may be some leeway here. DataFu and Aurora are in a similar position.