As of version 1.6.1 the URL for the minecraft_server.jar download has changed. This breaks auto server update scripts. It's OK to have URLs that point to specific versions, but please continue to have one URL that points to the current server version so we can continue to automate this chore. The old URL worked (https://s3.amazonaws.com/MinecraftDownload/launcher/minecraft_server.jar)

I don't mind so much if you create a new URL for this purpose but once created stick with it for the life of the game.