When you visit the http://localhost:8000 URL in your browser, you're executing your Symfony application in the dev environment. To visit your application in the prod environment, visit the http://localhost:8000/app.php URL instead. If you prefer to always show the dev environment in the URL, you can visit http://localhost:8000/app_dev.php URL.
There is no mention that app.php will 404 on both local and remote servers, and no mention of how to get it working. I've been reading countless message board posts for the last few hours trying to get it working. This is a terrible first impression.