Good catch! I think you are correct. As omegamon says, many agents don't expose the hrSWInstalled stuff but you should see the Software left-hand menu - even if it has nothing in it.
Check whether you can get data with
snmpwalk -v 1 -c public <your device> hrSWInstalled
substituting for <your device> and changing snmp version and community as appropriate.
If you get answers, then you should be able to get software.
You can run the modeler explicitly for software installed with
zenmodeler run -v 10 -d <your device> --collect HRSWInstalledMap
You should see data in the verbose output.
To check whether the modeling has actually worked, try using the ZMI (Zope Management Interface), by pointing your prowser at
http://<your zenoss>:8080/zport/dmd/manage
Drill down the servers into the instance of the device that you have modelled. Drill into os. Drill into software.
You should see entries for the installed software.
I think that proves the bug is in the software that displays information.
I have created a ticket for this - http://jira.zenoss.com/jira/browse/ZEN-8090
Cheers,
Jane