President Bush does hold a grudge (think Saddam Hussein), and has a killer instinct. He doesn't choose to "kill", however, in the conventional way. He can "kill with kindness" (think Ann Richards, when she called him "shrub" he treated her with respect; think Al Gore during the debates, when he got in George Bush's face Bush gave him a look up and down which was far more effective than punching him in the nose or throwing him off the stage.)
Think of Bill Clinton. George Bush refused to get into the mess re: Clinton's goons, er, staff destroying the White House. When the time came, after the Democrats made fools of themselves denying the story, the pictures were made public.
Just because George Bush doesn't avenge himself the way you or I would, doesn't mean he doesn't get revenge. Eventually.