Not sure why you're getting downvotes, for such a slick page basic email address form validation is an odd omission.
Strange, its still working as you mentioned earlier. What a weird bug to leave out in the open like that.
As long as you can receive a confirmation email, any address could work :)
But basic \S+@\S+ check on the UI side won't hurt and would be courteous.
But what if I worked at stripe and only wanted to type my username? :D
On this form it's less relevant, but that's very handy a lot of the time. I get frustrated when some outsourced app seems to believe that just sending mail to my username would not work, and refuses to let me do it.