You are right, there were three accounts, the admin and then the som and soc accounts at 10. At 10.1 there now only two accounts.
Can you perform a check for the name of the ArcGIS Server Account?
(Please don't make any changes and Cancel when finished.)
Start > All Programs > ArcGIS > ArcGIS 10.1 for Server > Configure ArcGIS Server Account
Is agsadmin the name listed for ArcGIS Server Account?
Click Cancel.
This account was created when ArcGIS 10.1 for Server got installed.
The other account (Primary Site Administrator) was created when the Site was created. To confirm this, do you log into ArcGIS Server Manager with agsadmin?