It is not public key stuff so the serial number would be the same for everyone who used the product in the time frame the cert was still valid and came with the download...just don't want people to start thinking every user would be getting a unique serial number for their own benefit.
It is a Web Server SSL Certificate
A Web Server SSL Certificate contains the following information:
The certificate holder's name,
The certificate's serial number and expiration date,
Copy of the certificate holder's public key,
The digital signature of the certificate-issuing authority.
Gladiator Security Forum