Unfortunately the parent item on both the fixed navbar and the navbar are not able to act as both a link and a dropdown anchor. This section was designed by the team at twitter bootstrap and has been designed in that way due to the rise in touch screen devices. For example people on a mobile wouldn't be able to click the link to activate the drop down menu as pressing the link would take them to the page.
Our classic nav however does allow this function, as well as some of the premium nav's in the Pagelines store. So you could swap out the fixed nav for the classic nav or use one the other navs in place to get this effect.