Java SE (Java Platform, Standard Edition)

The GTK+ look and feel classes seem to be missing from the Java 1.4.2 and Java 1.5 rt.jar file in the Windows JRE downloads.

They are in the 1.4.2 and 1.5 Windows SDK downloads.

I just now downloaded and installed the 1.4.2_08 Windows JRE and SDK packages;

j2re-1_4_2_08-windows-i586-p.exe
j2sdk-1_4_2_08-windows-i586-p-iftw.exe

If I run my application with the SDK it works fine.
If I run it with the JRE it can't find the GTK L&F classes;

C:\>java -version
java version "1.4.2_08"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_08-b03)
Java HotSpot(TM) Client VM (build 1.4.2_08-b03, mixed mode)

C:>c:\Program Files\Java\j2re1.4.2_08\bin\java -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel App

Exception in thread "main" java.lang.Error: can't load com.sun.java.swing.plaf.gtk.GTKLookAndFeel
at javax.swing.UIManager.initializeDefaultLAF(Unknown Source)
at javax.swing.UIManager.initialize(Unknown Source)
at javax.swing.UIManager.maybeInitialize(Unknown Source)
at javax.swing.UIManager.getUI(Unknown Source)

The rt.jar files are different between the JRE and SDK. The JRE rt.jar file is missing (at least) the GTK L&F classes.

Why is this?