Multiple times I've had someone complete a registration, only to find that they'd mistyped their own email address. Twice. Without their subsequent "Where's my confirmation?" email I might not have known, and they might never have completed their registration successfully.

It's a pain, but it's now reasonably familiar, and it serves a specific purpose - confirming the email address.

If you can get accurate details from people without requiring the explicit test of the explicit function then I'd be interested.