Just now I found out that users commenters to get a Google Blogger account before they can post comments to blogs hosted by Google Blogger.

This makes no sense. I wouldn't mind if they just required the commenter to register themselves and made creation of a blog optional. Yes, one could just create one and ignore it but it's irritating to be forced into creating and abandoning something like a blog just so I can post comments.
The right way to grow membership is by increasing the quality of service for members (i.e. convenience), not by telling blog readers to either join or go away. Maybe Evan or Jason can explain why.
Update:
It turns out that this was caused by a preference setting. Now it makes sense although I sure hope this was not the default setting. Evan and Jason, nevermind.