I have heard back from Edublogs and this is their reason for the difficulties.
The reason why that link is no longer working is that our sign-up page is now constantly moving it’s URL. This is part of the measures we had to implement to reduce splog creation (http://en.wikipedia.org/wiki/Spam_blog) on Edublogs.
Edublogs Support Team
Until a better arrangement can be made with Edublogs, I have removed the need to register to be able to make a comment. All comments will continue to be moderated by me before they are posted on our blog. I will be changing the instructions on our ‘Comments’ page soon to reflect these changes.