User blog comment:Jondanger23/why no up date/@comment-4565846-20120512000028

If you're going to update to 1.3 (or at least it's latest snapshot), please BACK UP your saves and original Minecraft.jar, because the newest version no longer uses the "saves" file and Minecraft.jar.

But... The game probably can't update itself to 1.3, due to the lack of Minecraft.jar.