That kind of explains it- improved gouge is on the first rank of the combat tree in wotlk, it's way further down in Cata so sub rogues didn't take it. A quick inspection of duelers on Warmane showed that some sub rogues take it and some don't on WOTLK.
I also found this video saying that improved gouge didn't allow restealths on retail but that it does on private servers:
https://www.youtube.com/watch?v=rRt4vpaiacY
I'll probably test it out in battlegrounds and stuff- if I see rogues getting restealths on me with gouges on my pet then I'll take a hard look at trinketing blind, assuming I even have it after deciding to eat a full kidney.