<p>Because most likely you have some <strong>favorite tags</strong> which might include <a href="http://superuser.com/questions/tagged/windows-7" class="post-tag" title="show questions tagged 'windows-7'" rel="tag">windows-7</a> </p>

<p>Then all questions about <a href="http://superuser.com/questions/tagged/windows-7" class="post-tag" title="show questions tagged 'windows-7'" rel="tag">windows-7</a> get highlighted on the site for you, because you're likely more interested in these</p>

<p>See this MSO question for more information: 
<a href="http://meta.stackexchange.com/questions/19173/what-do-favorite-tags-and-ignored-tags-do">What do “favorite tags” and “ignored tags” do?</a></p>

<p>For future reference, <a href="http://meta.stackexchange.com/questions/7931/faq-for-stack-exchange-sites">go have a look around the FAQ on MSO</a> it will most likely answer a lot of your questions</p>