If you happen to leave your computer unattended whilst you're logged in as an admin and someone sneaks onto your computer and types in the following...
http://your-website.com/wp-admin/options.php
They can see your unencrypted password!
How is this a security issue?
The reality is many people use the same password for other websites... it's one thing for someone to be able to sneak into your wordpress and CHANGE your password to a new one even if they don't know what your current one is... BUT it is another thing entirely for that sneaky person to be able to easily see your current password!
SURELY this is bad, very bad. There should be NO reason for my password to be visible and unencrypted even when I'm logged in.
By all means let me change my password but don't make it visible for crying out!
I'm sorry but saying "choose a unique password" doesn't cut it... the fact is many many many bloggers will be using the same password for their online banking.