I don't believe the package is including jar files at all.  The result of dpkg-deb -c on groovy_1.5.6-1 in intrepid show links to the libraries in /usr/share/java:

luis@trinity:~/dev/groovy$ dpkg-deb -c groovy_1.5.6-1_all.deb 
drwxr-xr-x root/root         0 2008-05-12 07:17 ./
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/doc/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/doc/groovy/
-rw-r--r-- root/root      3232 2008-05-12 07:16 ./usr/share/doc/groovy/README.Debian
-rw-r--r-- root/root      2223 2008-05-12 07:16 ./usr/share/doc/groovy/copyright
-rw-r--r-- root/root      1421 2008-05-12 07:16 ./usr/share/doc/groovy/changelog.Debian.gz
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/man/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/man/man1/
-rw-r--r-- root/root       874 2008-05-12 07:17 ./usr/share/man/man1/groovy.1.gz
-rw-r--r-- root/root       451 2008-05-12 07:17 ./usr/share/man/man1/groovyc.1.gz
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/groovy/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/groovy/bin/
-rwxr-xr-x root/root       759 2008-05-12 07:17 ./usr/share/groovy/bin/groovy
-rwxr-xr-x root/root       605 2008-05-12 07:17 ./usr/share/groovy/bin/groovyConsole
-rwxr-xr-x root/root       626 2008-05-12 07:17 ./usr/share/groovy/bin/groovyc
-rwxr-xr-x root/root       714 2008-05-12 07:17 ./usr/share/groovy/bin/groovysh
-rwxr-xr-x root/root       633 2008-05-12 07:17 ./usr/share/groovy/bin/java2groovy
-rwxr-xr-x root/root      8009 2008-05-12 07:17 ./usr/share/groovy/bin/startGroovy
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/groovy/conf/
-rw-r--r-- root/root       892 2008-04-25 12:26 ./usr/share/groovy/conf/groovy-starter.conf
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/
-rw-r--r-- root/root   2304286 2008-05-12 07:17 ./usr/share/groovy/lib/groovy-1.5.6.jar
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/share/java/
drwxr-xr-x root/root         0 2008-05-12 07:17 ./usr/bin/
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/man/man1/startGroovy.1.gz -> groovy.1.gz
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/man/man1/groovyConsole.1.gz -> groovy.1.gz
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/man/man1/java2groovy.1.gz -> groovy.1.gz
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/man/man1/groovysh.1.gz -> groovy.1.gz
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/xpp3.jar -> ../../java/xpp3.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/xstream.jar -> ../../java/xstream.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/servlet-api.jar -> ../../java/servlet-api.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/regexp.jar -> ../../java/regexp.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/mx4j.jar -> ../../java/mx4j.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/mockobjects-core.jar -> ../../java/mockobjects-core.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/jsp-api.jar -> ../../java/jsp-api.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/junit4.jar -> ../../java/junit4.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/jline.jar -> ../../java/jline.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/commons-logging.jar -> ../../java/commons-logging.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/commons-cli.jar -> ../../java/commons-cli.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/classworlds-1.0.jar -> ../../java/classworlds.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/bsf.jar -> ../../java/bsf.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/asm2-util.jar -> ../../java/asm2-util.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/asm2-tree.jar -> ../../java/asm2-tree.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/asm2-analysis.jar -> ../../java/asm2-analysis.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/asm2.jar -> ../../java/asm2.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/antlr.jar -> ../../java/antlr.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/ant-launcher.jar -> ../../java/ant-launcher.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/ant-junit.jar -> ../../java/ant-junit.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/groovy/lib/ant.jar -> ../../java/ant.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/share/java/groovy.jar -> ../groovy/lib/groovy-1.5.6.jar
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/startGroovy -> ../share/groovy/bin/startGroovy
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/java2groovy -> ../share/groovy/bin/java2groovy
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/groovysh -> ../share/groovy/bin/groovysh
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/groovyConsole -> ../share/groovy/bin/groovyConsole
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/groovyc -> ../share/groovy/bin/groovyc
lrwxrwxrwx root/root         0 2008-05-12 07:17 ./usr/bin/groovy -> ../share/groovy/bin/groovy