I suppose age is the biggest reason, though the San Antonio Spurs, a relatively similar team except their Center is an offensive and defensive powerhouse, have aged perfectly well (see this). The largest reason is the offseason recruitments of first Allen Iverson (which was mostly to clear contract space), and then having gotten a crapload of space the further acquisitions of Ben Gordon and Charlie Villenueva.
The biggest issue they had was having payroll space the offseason before Lebron/Wade/Stoudemire etc. hit free agency, so they had to pick up flawed players. Ben Gordon and Villenueva are both purely offensive players, Detroit has played tough defense as their MO since the dawn of time, so naturally they do not function well in the environment, just as Iverson did not.
So then, what is the chance for recovery if any? The pistons need to trade their dead weight within a few seasons and acquire another marquee player, or rebuild from the inside with solid draft classes. Joe Dumars had been an excellent GM up until 2008 (sans the Darko Milicic fiasco) and everyone did applaud the Iverson trade due to the nature of NBA contracts.
The salary floor in the NBA is so high that terrible contracts become a resource to free up cap space before impending free agency. You can't simply run out a terrible, cheap team most of the time as in baseball. Of course as a result of this many of the NBA franchises are losing money every year, as no one watches the NBA and filling even a small arena for a terrible team is unlikely. The NBA was nearing bankruptcy a year ago though perhaps the newly successful Knicks and Heat will change that.
It looks like the best the pistons can hope for for the next 3-4 years is .500 and barely making the playoffs. As I've said before barely any teams are at 500, they're either really good or really bad with very little inbetween, but that doesn't mean the Pistons can not achieve that. After that perhaps they can actually attract a good free agent as opposed to the terrible situation they're in now. Even a terrible team like Miami can attract FA's in the NBA so I don't think it'd be too much of an issue with the Pistons' storied history.
Aside: I've started playing Red Dead in addition to the other 3 PS3 games mentioned, pretty damn awesome and a hell of a lot better than GTA IV.