I've always found it to be supremely annoying to have to enter an email twice -- except for the one or two times that it caught an error. Maybe a better question would be: why are email addresses usually ***'d out? What harm would it be to have it visible in plain text, as the price for having to enter it only once? Of course, that doesn't guarantee that someone won't make a typo entering it, but there's a chance of catching it visually. They can make the same typo entering it a second time (I do a one-finger hunt-and-peck for the second entry), or copy and paste the first entry into the second (accomplishing nothing).
I don't understand the question about email confirmation instead of entering it twice -- if you got the email address wrong the first (and only) time, that's all she wrote -- the confirmation will go to the wrong place (possibly to no one). Verifying through DNS, if that works, merely tells you there's a legal address on the other end, not that it's going to the supposed recipient.
I vaguely recall this very matter being discussed several years ago. You might want to do some searching for that discussion.