Blogger is messing us about again. Recent changes to the comment facility has resulted in the disappearance of the ability to subscribe to a comment thread if you have your comment settings set to pop up window. However, it is still there if you set your comments to "embedded beneath post."
I strongly suggest that we all change our settings to embedded. Otherwise there will be no conversations on our blogs anymore and a drastic reduction in visits.
Thanks to Grandmère Mimi for sussing this one out for us.