nesting instead of id ing

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I am looking at the site template here: /
The Nav menu is in the html like this:

     <h2>Menu </h2>
         <li><a href="index.html">home</a></li>
                 <li><a href="#">about us</a></li>
                 <li><a href="#">blogs</a></li>
                 <li><a href="#">arcade</a></li>
                 <li><a href="#">gallery</a></li>
                 <li><a href="#">links</a></li>
                 <li><a href="#">contact us</a></li>
                 <li><a href="#">forums</a></li>

And the Nav has no id but is selected in the css as
     #sidebar li li

I realise the futility of sometimes looking for purpose and design in a
world in which meaning is almost always elusive but here is my question:
Is it normal or common this nesting of lists instead of giving them a
class or an id? I have never seen it before. And Why?

Tim W

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