Okay, it looks like it isn't really a case of "extending the core talk table". All of the talk tables loaded by the game go into one big talk table, so when you're creating a module with new abilities in it you should put the ability names into the module's talk table. I'm just looking at some of the abilities added by the Grey Warden Base 2DA and their strings are in the Grey Warden Base talk table. They're set to string type "Talent", that might be something to look at - as far as I'm aware the string type is for organizational purposes only, but perhaps GUI-related stuff is special and actually cares about that.
The core talk table's stringIDs match up when I compare the end user toolset's core talk table and the development talk table, and with the 2DA entries, at least at a quick glance. Chronovore and andyr1986 (or anyone else for that matter), when you say that the string table and 2DA stringIDs don't match up, could you give me an example?