"Usually later versions will either completely supersede or incorporate earlier versions, so there is generally no point in keeping old versions around" (from http://www.catb.org/~esr/jargon/html/revision-history.html)
The answer is that I do believe it's worthwhile to save these old versions. Language, particularly slang, changes all the time, and while most people are concerned with the current version, it can be fascinating to look into its history. The older versions, far from being obsolete, give enlightening glimpses of the way hackers spoke, thought, lived and worked in days gone by. Furthermore, the claim that newer versions completely incorporate the older ones is not completely accurate, as "dead" entries are routinely pruned out.
Interestingly, Eric Raymond is now rather more open than previously about the history of the File. When I first set up this site, the only officially-available Jargon File was the most recent one. Now, though, the official download page contains a link to older versions and a list of deleted entries.
The Jargon File says (or said) that the metasyntactic variable 'corge' came from the name of a cat, and was invented by Mike Gallaher. FOLDOC, however, states that Corge was fictional (possibly through bad punctuation or a misunderstanding of the original Jargon File entry).
So it was with a some surprise that, during my travels on the Web one day, I came across the home page of Corge's owner. Let it be known that Corge was, once upon a time, a real cat. (The older home page on apocalypse.org is no more, but here is a link to an archived version)