Based on this thread: http://social.microsoft.com/Forums/en-US/cc444c7a-a838-4a16-ac57-8f315475b602/how-does-one-reply-to-a-post-i-see-no-reply-button?forum=reportabug
It seems that for locked threads, people can scroll past the the "Lock" icon too quickly to realize, and then not understand why they can't reply. I
Instead of hiding the reply link, I suggest changing the "reply" text to "Locked" for locked threads, and have it not be a hyperlink.
Thanks,
Mike
MSDN and TechNet Subscriptions Support