I just found this on Skittles' Place from Blogger:
Just before the weekend we added the final piece to the transition from old Blogger to the new Blogger in beta: members of team blogs can now switch to the new Blogger. This is the last step before we take the new Blogger out of beta. This all means that we’ll be removing the “beta” from the new Blogger very soon! At that time, we’ll begin the process of requiring that users of old Blogger move to new Blogger.
So evidently all users of the old Blogger will soon have to move to the new one. I know some people don't like the beta blogger for various reasons, but I do. I think it's better than the old one, more user friendly. So come on over to the dark side! Resistance is futile!