The CLASSPATH in Java is a horribly broken concept, IMHO. For instance, did you know there's more than one CLASSPATH? There's the normal CLASSPATH and a "boot CLASSPATH". You hardly ever have to care about that, but when you do, confusion ensues. Not to mention all of the other nightmares involved that you can easily find by Googling on Bing. In fact, it's such a pain that tools like JWhich were created to help you figure out what's going on.
Sharing binaries seemed like a good idea in the 90s, but I think we're mostly in agreement that XCopy is the way to go today.