Despite some similarities, you should not confuse the two. Visit the Sun Microsystems site to learn more about Java. Because the majority of action occurs locally, fewer packets of data transfer are required. This conserves bandwidth. More and more users means more and more traffic.
More traffic can result in slowdowns for everyone.
Even if the bandwidth problems are resolved with advances in hardware and technology, you, as a Web Developer, don't want to annoy visitors to your site by burdening them with huge downloads of data. All the JavaScripts and the newsletter are free. You can use the scripts as an amateur on your own pages, or as a professional on your clients' pages. The hope being, of course, that at some point you will be motivated to visit their pages. Time you spend modifying a script or incorporating it with other elements on a page can, of course, be billed.