It's hard to imagine that that was a big enough problem to warrant this kind of action. The problem is, people who have an old, forgotten Gravatar account aren't going to go through the whole resetting the password thing just to be able to comment on WP blogs. I've already had an e-mail from a regular reader who got the "you must log in" message, knew she didn't have a WP account, probably registered a Gravatar account at some point, but she's an older lady from another country, and if she understood my explanation of it all, she's not going to bother with all that. She'll probably just e-mail me her comments from now on, and I don't mind that, but it takes away from the conversation on the blog itself a bit, and most commenters probably are just going to pass on commenting when they run up against an obstacle of any kind. I know I can disable the e-mail requirement, but I like having a way to respond to commenters, plus having the e-mail requirement there seems to cut down on spam comments
I think this and changing the default setting to automatically subscribe commenters to replies are just going to irritate readers and cut down on the comments WP bloggers receive.