That is by design. What happens is that those top level links only fire if javascript is disabled. If you go with it like that, they can be a backup for non-javascript enabled browsers - for accessibility purposes - say, they could take the non-javascript user to a page with a menu that has the same links on it that the drop down has.
However, depending upon the overall design of the pages and links involved, like if all of the links on a drop down are to anchors on a single page, you might want the top link to also be to that page, and to have it fire even when javascript is enabled.
Now, this obviously makes no sense if the drop down activates onclick, you'd never see it. But, for drop downs that activate onmouseover, simply remove this (highlighted) from the link:
Code:
<a href="default.htm" onClick="return clickreturnvalue()" onMouseover="dropdownmenu(this, event, menu1, '150px')" onMouseout="delayhidemenu()">Web Design</a>
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