Running mvn org.apache.maven.plugins:maven-dependency-plugin:2.10:sources -DexcludeTypes=pom on built spring-kitchensink-basic quickstart results in as follows:

[INFO] The following files have NOT been resolved:
[INFO]    com.sun:tools:jar:sources:1.7:system

it is worth noting the fact that the QS functionality is not affected. But it's better to get rid of this non-resolvable dependency source file.