Must Bootstrap container elements include row elements?

The .row class is not required inside a .container, but it is a good idea to include it anyways when you start incase you want multiple rows later on.

All that .row really does is make sure that all of the divs inside of it appear on their own line, separated from the previous and the following .rows.

For the .container inside of the .navbar divs, that is a separate thing that is required to make the navbar line up with the rest of the page. If you look further down in the rendered HTML, you'll see that there is another .container that is not inside any .navbar divs, and that is the one with all of the main content.

A Complete Example

<div class="container">
  <div class="row">
    <!-- These divs are inline and do NOT fill up the full 12 columns -->
    <div class="span4">...</div>
    <div class="span4">...</div>
  </div>

  <!-- This is a automatically a new line of divs -->
  <div class="row">
    <!-- This div will appear below the previous row, even though it
      would fit next to the other divs -->
    <div class="span4"></div>
  </div>

  <!-- These will appear in their own row, but may act
    unexpectedly in certain situations -->
  <div class="span4"></div>
  <div class="span4"></div>
</div>

In Short

.row defines a row of divs, like the name implies. Each one indicates a new line of divs, no matter if the above line is full or not.

The answer is much simpler than those given. No, .container does not have to contain any specific code, and it has no encumbrances on what contains it...

What .container does is serve as a "wrapper" to "contain" the size of any and all elements wrapped inside of it. And .container can wrap pages or components. So, if you want a page similar to those Twitter Bootstrap's docs, with a "fixed" width and equal margin on both sides, then only a single .container is necessary to wrap all of the content on the page.

There are other uses for .container as well; have you noticed how the top navbar in Bootstrap's docs (.navbar-fixed-top) spans the full width of the screen, but the nav items inside the navbar are "contained" to the width of the content? This is because the .navbar-fixed-top is not inside a .container but the .nav inside it is.

The bootstrap grid is composed of 12 columns that can be adjusted in any combination within a row as long as they add up to 12. You can think of them as containment rows such as the likes of table rows, which are meant to separate different rows of content. Within the grid, the .row container has a separate task and is there (and required) to readjust the last grid columns gutter width, which varies depending on screen size (if the responsive sheet is included). If you look at the css behind the .row class you will notice that it has a property of margin-left:-30px by default (once again it can be greater or less depending on screen size), a property which is meant to "remove" the gutter from the last column in the row; without it the grid would not readjust the gutter and it would break onto a second line.

Now, the reason why the .row container is a child of the .container container is because the .row container is only meant to separate "lines" of content, not to contain sections and more over center content in a page. As such, the reason why the navigation example did not have one was probably due to the fact that the nav elements is lacking in gutter width, since it was meant to be a full block element and not a grid, so there was no need to reset that last loose gutter.