I don't think I've ever seen one that wasn't paste-disabled, though my knowledge is way out of date since I found out about the aforementioned config setting.
It was definitely a case of a PM coming up with a quick and cheap 'fix' to the problem of getting so many people typing their email address wrong the first time.
We (from the tech side) put together a bunch of options, including validating the domain and giving the user feedback if delivery doesn't succeed immediately.
But it was put on a backlog of 'nice things to implement' and never delivered.