From the changelog:
Changed all visible instances of blog to weblog in the system and in the documentation.
I’ve hated the word “blog” since the day I first heard it.
Movable Type Pro sounds good too. Especially the bit about allowing users to log in for comments. Pepys’ Diary uses huge numbers of comments (around 1,600 in six weeks) and anything that beefs this facility up will be a boon.