There are two different versions of GoToWebinar. The new one is called Global GoToWebinar and it has the new user interface. I've been told by the Product Manager at GoToWebinar that they will be adding the ability to turn on/off the confirmation emails in Q1. I've asked for more specific details and will let you know when I have more information.
If you are using the legacy GTW, then you still have the ability to turn on/off the confirmation emails. One way to distinguish is to look at the URL. If you are on global GTW, the URL will be global.gotowebinar.com. If you are on the "old" gotowebinar, then your URL will start with wwwX.gotomeeting........