When testing Java Web Start for Tiger, jdk1.5.0 B02, I found the Platform Version shown in the JaWS Application Manager was 1.4. After investigation, I found the root cause of this problem was that Tiger showed following incorrect info: "java.specification.version=1.4".

STEP TO REPRODUCE:
1. Install JRE1.5.0
2. Enable Java Console
3. Go to http://java.sun.com/applets and launch any of the applet demo
4. Press "s" to dump system properties.
5. You will see the following from Java Console:

java.runtime.version = 1.5.0-beta-b02
java.specification.version = 1.4
java.version = 1.5.0-beta
java.vm.version = 1.5.0-beta-b02
java.vm.specification.version = 1.0
javaplugin.version = 1.5.0