Hello,
Are you talking about SEP 12.0 or SEP 12.1 ??
I believe you have already created a Thread on Symantec Forums:
https://www-secure.symantec.com/connect/forums/sep-100-and-sep-120-virus-pattern-difference
There is a lot of difference between the Symantec Antivirus 10 and Symantec Endpoint Protection 12.1.
The major difference is these are 2 different products having different features.
SAV 10.x - Symantec Antivirus
http://www.symantec.com/security_response/definitions.jsp?pid=scs
SEP 11/12.x - Symantec Endpoint Protection (Includes Antivirus, Host Firewall, HIPS,App & Dev Control,TruScan etc)
http://www.symantec.com/security_response/definitions.jsp?pid=sep11_32
http://www.symantec.com/security_response/definitions.jsp?pid=sep1213
So its not just Architecture but SAV was just simply antivirus but SEP is complete Endpoint Solution for Endpoints.
Secondly, SAV 10 is a End of Support Life (EOSL) product.
End of Life announcement for Symantec AntiVirus Corporate Edition and Symantec Client Security
http://www.symantec.com/docs/TECH178551
Symantec Antivirus Corporate Edition vs Symantec Endpoint Protection
https://www-secure.symantec.com/connect/articles/symantec-antivirus-corporate-edition-vs-symantec-endpoint-protection
I would recommend you to run the current Latest version of SEP product . i.e; SEP 12.1.3001
Hope that helps!!