"I cannot tell that they have any different status than questions"
What you actually mean is "I cannot tell, just by looking at the navigation panel, that ..." - unless you hover your mouse over it and get a tool-tip. Of course you can see on the right that 4 and 5 are not yet answered.
I don't think it is any help for you to link me to generic W3C guidelines. If you want to convince me to solve this, get out Photoshop (or similar) and amend the screen-grab of high-contrast mode (and make the corresponding changes in normal mode) to show me an effective graphic design that solves this 'problem' and looks nice.
Actually, I know half a potential solutions. See http://moodle.org/mod/forum/discuss.php?d=183604. The only problems are that the way the OU theme is currently implemented does not work in Windows high-contrast mode. It uses background images which disappear. That could possibly be fixed. The other problem is that changing this could piss off all theme designers.