Some time ago I discovered that dropdown menus that do have clickable links on parent nodes are confusing for the users.
Often they are not seeing that they can click on the parent, they just assume that the parent is just like a folder.
Check yourself the demo from http://2010dev.wordpress.com/ – see the second menu item, named “parent page”. This is clickable but it may be not so obvious for many people.
Also, this approach impose some issues with touch based devices where people may find impossible or hard to click a submenu-item.
I would like to see a solution for this problem, but not one that would require me to fully change the theme.
This is a known issue with the Twenty Ten theme, arising from both the theme and core code. Twenty Ten has a number of accessibility issues – see Trac: http://core.trac.wordpress.org/ticket/14782
Some of these have been corrected in a child theme for Twenty Ten that you can get here: http://accessible.sprungmarker.de/2011/01/accessible-1-0/ The CSS and functions in the child theme cannot correct the menu issues though.
Unfortunately, the menu issues are still present in the new Twenty Eleven theme that is coming with WordPress 3.2.