According to Baseball Prospectus though, Davey had never meant that the closer was part of the A and B designations, rather everyone else that pitched before the closer would tend to fit in one group or the other so he could easily keep track of guys getting enough off days for rest. While I can't tell you if that in itself is true(sounds like a fun correlation exercise though!), a simple look at last season will tell you Davey doesn't usually rotate closers. When H-Rod lost the job to Clippard, Clippard took all the save opportunities. When Storen came back from injury he was first not the closer, and then he won the job back. At no point was there a committee where Clippard got a chance, then Storen, and repeat. So why do some people think of it as something else? Two reasons.
At the beginning of last year remember, the Nats had NO closer. Davey was determined to keep Clippard pitching the 8th (for some reason), so both Lidge and H-Rod were put in as closers. In this scenario, Davey did indeed rotate save chances... for about a month until Lidge proved completely unworthy. So it certainly seemed that this new coach that talked about A and B pens meant it as rotating closers if he felt he had the talent. Adding to the confusion was Rizzo sort of saying as much, when talking about the Nats situation.
Just as a for instance, Davey has what we call an A/B bullpen. Instead of being locked into one guy as your closer, or your seventh- or eighth-inning guy, he makes sure he has a B guy who can step into that role in case the A guy can't go.Now really you shouldn't interpret that as being a committee but rather a secondary guy who gets closing scraps if the closer has worked too many games. But if you were already inclined to think of the A/B plan as a "one then the other" situation, you could read this in a way to back you up.
The second reason is that he DID do this. Back in the mid 80s with the Mets, Davey did use two closers fairly regularly. Take a look at the 1st and 2nd guys in save opportunities over his first five years managing :
1984 : 39, 18
1985 : 25, 23
1986 : 29, 28
1987 : 32, 22
1988 : 29, 20
(Another thing - most of this was a lefty/righty thing which doesn't apply to the 2013 Nats)
But by early in 1989 McDowell and Orosco, who were big parts of these scenarios would be gone and for the rest of his managerial career Davey clearly favored one guy and only in 1994 would he come close to trying to mix it up again
1989 : 29, 11
1990 : 39, 5
1993 : 28, 12*
1994 : 21, 11, 8
1995 : 32, 9
1996 : 38, 8
1997 : 46, 10
1999 : 39, 5
2000 : 34, 7
2011 : 48, 11
*If this looks a little fishy to you Dibble got injured in 1993 and missed time and that's when Jeff Reardon got 8 of his 12 save opportunities. Otherwise Dibble was it
This is all just a roundabout way of saying that you shouldn't expect Storen to get more than a handful of opportunities to close if Soriano is healthy and effective. I would probably bet on something in the single digits.