As I've mentioned by default div is a block level element without any doubt. But it is possible to convert a block level element like a div element to an inline element using CSS.
In such situation if the user have to examine both CSS and (X)HTML source to find which are acting as full-fledged block level elements and as inline elements.
So in order to avoid such confusion in such situations I've phrased it as "usually".
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title> </title>
<style type="text/css">
.inlinediv{
display: inline;
}
</style>
<script type="text/javascript">
</script>
</head>
<body>
<div>Test </div>
<span>This is a </span><div class="inlinediv">test</div>
</body>
</html>
In the above case the highlighted <div> element will not have any preceding and succeeding line breaks.