There is a bit of traffic that comes to the wikipedia.org portal that has the HTTP referrer 'wikipedia.org'. This implies that the page is somehow redirecting traffic to itself.
@ksmith noted these lines in the source code of the portal page might be the reason and it'd be interesting to know if it really is:
<!-- Search form -->
<div class="search-container">
<form class="pure-form" id="search-form" action="//www.wikipedia.org/search-redirect.php" data-el-section="search">
<fieldset>