Great idea, and great to find it perform better. It probably helps alleviate the confusion some people feel inherent in dealing with their computer - the same kind of people who have no idea how to respond to a dialog box with yes/no|accept/decline, but can answer the same question promptly when posed verbally.
It's nice to see an actual implementation - and that it's not a conversion killer or anything.
But it would be nice to see a clearer example of it being the only change to a form.
Right now it looks as if it's only optional in the "after" form. And then it's quite obvious why it converts better.