The loss of Jerome Bettis is certainly something to consider - most Steelers fans I talk to have a slightly different take on the whole thing. I lean toward the idea that his leadership is missed most, while my Dad insists that just having Bettis on the team in the 4th quarter of football games was huge. A tired defense does not want to see a back like Bettis lumbering at them, that's for sure. Parker certainly doesn't bring that factor to the running game, so maybe my old man is on to something.
And yes, the Steelers only went 11-5 last year, but two of those losses occured with Tommy Maddox at the helm of close games. Not a recipe for success. Ben was outstanding for the majority of last season, so it's not too much of a stretch to say that they weren't your average sixth seed heading into the playoffs.
This year, the problems tend to center around an offense that is in genuine disarray, a defense plays well for the most part but struggles to get the timely stop, and some pretty stupid mistakes at bad times in games (i.e. the muffed punt vs. the Bengals, or any of a number of Ben's mind-boggling interceptions). The majority of the fault probably lies with the offense - if they can start to establish a consistent running game and Ben can get back to playing efficient football, I think a lot will be solved. Whether that will happen...at this point, who knows.