Soriano has a few mental qualities that you want in a closer - a) he's fearless; b) he is not afraid to fail; c) he has a short memory regarding the last batter/game, etc.
The best reliever isn't needed to be the closer, because closing games is more a matter of simple math most of the time. A closer with mediocre stuff will get a bulk of his saves simply because the odds are in his favor, especially with more than a one run lead, and will probably blow a few here and there when the first guy gets on base in a one-run lead -- assuming he has the courage to throw strikes. Pitching behind and walking guys is the sin, and that's what really cost him.
Unfortanately, Soriano doesn't have the stuff to match the swagger, but just by attacking guys has gotten him by. It's the same reason Capps was successful here while a spaz like Hanrahan was not.
If only we could perform a brain transplant and put Soriano's head on Storen's body, the team would be so much better off. Last night's game was like watching Game 5 all over again with the 0-2 counts with two outs wasted. And when it comes to wasting money, 28M on Soriano comes to mind. The guy certainly gets by with a decent Save % when he's pounding the zone, but he isn't worth that money, because he simply isn't a guy you would feel confident winning a title with. You need the mind and the stuff. To me, he's a really expensive Matt Capps, except Soriano's a dick.