Ought to agreee with CC on this one; the execution of defeated leaders after a triumph seems to have been regular practice, and Pompeius was certainly bloodthirsty when required.
In fact, Imperial historians tended to consider both CJ Caesar and Cn Pompeius Magnus too soft for their taste.
It certainly was regular practice. It just wasn't something Pompey indulged in. I can't remember if I read that in Goldsworthy, Heather, or Holland though. He was horrible in other ways, just like the rest of them, but this was his one saving grace. In fact, here is part of Appian's description of a Pompeian triumph:
"His chariot was followed by the officers who had shared the campaigns with him, some on horseback and others on foot. When he arrived at the Capitol he did not put any of the prisoners to death as had been the custom at other triumphs, but sent them all home at the public expense, except the kings. Of these Aristobulus alone was shortly put to death and Tigranes somewhat later. Such was the character of Pompey's triumph."