I Disagree. They can't reliably get information on what addresses work from the transport mechanisms. The Mail Exchanger (MX) for any given domain may simply be a relay, and unable to tell the remote host if the/a recipient is invalid. If your MX is able to give that information, or is a relay that can do so by using LDAP lookups, I'd be surprised if the spambot actually cared about recording the status of that particular e-mail address (a lead, if you want to make it sound nice).
Now, in the case that you have a relay, every message will get an OK status when the spambot delivers the message. When the message gets to a host that can say if the recipient is invalid, the relay that was connected to that host will make the "bounce" message -- I'll say "DSN" here. DSNs are sent to the envelope sender of the message. There's a very slim chance that the envelope sender of a spam message goes to some mailbox that tracks the status of leads. That would make blocking spam messages much easier for us Good Guys. Most of the time, they will use an invalid user at a valid domain. Sometimes, the user is valid. That's called a Joe Job, and the user or domain will start receiving thousands of DSNs for messages that they never sent. Not fun at all.
I think that in this case, it's simply a mistake on the spammer's part. That sort of thing is rather common -- most often, I see messages that have a bunch of tokens that are meant to be substituted before the message goes out, but aren't. I've seen some other stupid ones before, too.
mhoward - at - hattmoward.org