My friend, MadPriest, posted the following:
"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."
So, I'm off to change all those settings right now.