[Black Tiger]

I don't understand, can't you just turn on "Verify Email address in Registration" option in the AdminCP to prevent users with bogus email addresses from creating accounts to begin with?

Which part don't you understand? It's the same as other bounced emails.
This option you mention is turned on. The "verify email address in registration" does nothing else then send you an activation email als registering user.

An example:
Suppose you register at my forums and you make a typo in your email adres or put in a fake email adres like idont@wantmail.com, then a verification email is send to that address.
Since the address does not exists, the email get's bounced as being undeliverable.

It's just the same as with birthday email's or thread subscribtions, emails are getting bounced.

Depending on the bounce reason stated in the bounced mail, I can then choose to have users account adjusted, which your hack does, or get users account deleted which was my suggestion.