The regular torpedoes were never "accurate" unless a target was standing still, or if the shooter was close enough, the shootee could be slow moving. That would be my guess as to why they didn't. If you can get the AI to target correctly, you'd be famous, maybe even infamous...
As for the dropped torpedoes, the homing ones did not work from the airplanes for whatever reason in a lot of tries, but someone did it... where is that confounded thread?... Can't find it real quick, but it was Rubini in SH3:
Hah! found the thread:
http://www.subsim.com/radioroom/showthread.php?t=197919
and the release thread:
http://www.subsim.com/radioroom/showthread.php?t=197762
I'm not sure what all it takes to convert it to SH4 compatibility. Now, if you could get an AI ship / sub to shoot one of those, "modded" to go normal torp speed, who'd need 'proper' targeting?... Look-out!