I can't believe Martinez survived the return from the roadtrip, but this is the Lerners. They don't do anything that other baseball teams would do, because they hate cutting ties with anything they have already paid for (e.g. Rosenthal).
But regardless of all the reasons it makes sense to dump Davy, Rizzo should be fired for this bullpen situation, and the Lerners should be ashamed of their cheapness. With three top caliber starters in the rotation, you have to have a bridge to your closer. The 8th inning has been the complete undoing of this team. An average team gives up .5 runs an inning. The Nats 8th inning stat is a historically awful 1.02. An average performance from a reliable 8th inning reliever would reduce the run differential by 25 runs and have them around .500 ball with the Mets. Given that they have melted down in so many divisional games, who knows how that would have panned out. Not investing in one if not two reliable set up guys to handle the bridge to the closer is unforgivable. Lerners just don't get it, and it appears Rizzo is either incapable of understanding the importance of a bullpen or has never been able to convince the Lerners otherwise. He has had that reputation across the league for years, and now he is seeing its worst effects.