Also, Sonnen may have not many tko's on his record, but the dude is strong as hell. A guy like that pounding on you is always the right couple punches away from ending a fight... especially when you're in his zone of expertise. I'm not talking about a lucky haymaker.
Sonnen may be strong as hell for wrestling, but that doesn't necessarily mean he can translate that strength into striking, because it's technique that translates the potential strength into factual strength. And in that fight, most of Sonnen's punches were hammerfists thrown from the elbow only, there was no body weight behind them and so there was no KO power in them, not even close. Actually, if you train for full contact fighting, you regularly get hit harder in sparring than by most of Sonnen's punches in that fight.
So, yes, Silva was in danger to lose by decision, no doubt about the scorecards being 40-36 or worse against him until the submission, but he was never even close to getting (T)KOed.