Yeah, it looks like that. jQuery rebuilt their plugins web site some time ago, and then may have cleaned up some older plugins.
HTML5 now has built-in support for watermarks using the placeholder attribute, minimizing the need for plugins like this one. In my recent 4.5.1 update of this book, I dropped the plugin and just used this placeholder. If you want to support browsers that don't support the placeholder, you can take a look at this alternative plugin: http://plugins.jquery.com/watermark/
Note: I don't have experience with this specific plugin.