LHW Stuart Austin manhandled and broke Tom, despite a THIRTY POUND size disadvantage. Imagine getting bitched around by a guy 30 lbs lighter in what is Tom's base, grappling, what he had already been training since childhood, and where size is such a huge asset. So don't bother with the excuse that it was a long time ago.
Sometimes shit happens in fights, Serra knocked out GSP. But like you already proved, Gane showed the heart and grit to deal with that adversity when Tai landed the fluke bomb (with Tai being one of the hardest hitters, power and chin are the only reason he's even UFC level) to come back and stop Tai in his tracks.
Gane actually BRAWLED after Tai landed that, just to prove a point, and finished his ass. He wanted to completely beta Tai and show him that he could outdo him in the only thing Tai is good at.
Tom on the other hand broke the one time he faced adversity in a fight. That's the difference.