To clarify the above: CraftBukkit is essentially a breakdown and rebuild of the Minecraft server jar. It gets "re-coded" in order to add in API. Once a Minecraft version is released (for instance, 1.1), the Bukkit team takes it and works on it until they can make a release (1.1R1, R2, R3, R4). Along the way, they release builds in order to get community feedback on what's gone wrong, before they make something a release build. Because of it's ever changing nature, the Bukkit team won't do anything with Snapshots, since they're not even a full Minecraft release. Once Minecraft 1.2 actually comes out, the team will just go hard at it in order to release 1.2R1 (but it takes some time, and will probably take quite a while with all of the changes Jeb is making...).
Thanks, rockingoutloud That pretty much sums things up. There's little point in spending the many hours required to update to a snapshot that very few users will utilize (most just wait until the Update button shows up) and will change before the proper release.
