title: How come some site urls do not include a file extension?
body: <p>I was browsing the internet and noticed, YouTube, for example, contains a URL like this to denote a video page: <code>http://www.youtube.com/watch?v=gwS1tGLB0vc</code>.</p>
  
  <p>My site uses a URL like this for a topic page: <code>http://www.example.com/page.php?topic_id=6f3246d0sdf42c2jb67abba60ce33d5cc</code>.</p>
  
  <p>The difference is, if you haven't already noticed that on youtube, there is no file extension for their watch page, so I am wondering, <em>why do some sites not use file extensions and what use does it serve?</em></p>