I went back and reviewed teams between 1999-2008 who had a top-10 scoring defense and a top-10 rushing offense (total yards) to see generally how those teams performed (record wise), whether they made the playoffs, and whether they made or won the Super Bowl.
There were a total of 45 teams in those 10 seasons. The season by season breakdown is fairly constant, with a low of 3 teams (2001) and a high of 6 teams (2000; 2005). Nine of those teams (i.e. 20%) failed to make the playoffs, so clearly good defense and running the ball will get you into the playoffs generally. One of those 9 teams was the 2000 Steelers (9-7), and of those 9 teams only the 2002 Jags has a sub-.500 record.
The Super Bowl is a completely different story. Of the 20 Super Bowl participants during that period, only 5 used the defense/running formula. Those five were Baltimore in 2000 (W), St Louis in 2001 (L), Carolina in 2003 (L), New England in 2004 (W), and the Steelers in 2005. Especially notable is in recent years nobody has used the defense/running formula since 2005 - including the 2008 Steelers, the 2007 Giants and both the 2009 Colts and Saints.
Overall, based on recent results, the idea that you can use a system QB, good defense, and good running to win a Super Bowl is really small. The only clear example of that occurring is the 2000 Ravens - which gives you less than a 10% success rate. It doesn't work particularly well in getting a team to the Super Bowl either. The formula does work well in avoiding losing seasons and getting into the playoffs.
In terms of the Steelers, the best season compiled during that 10 year period by any team was the 2004 Steelers - where the Steelers used the second ranked rushing offense and the best defense to go 15-1. At that point Ben probably was indeed a system QB. The following year the Steelers had the 5th ranked rushing offense and the 4th ranked defense - both dropping from the previous year - which seems to be implying that you need a fairly high level of QB play to do well and that the Steelers were already relying on Ben to win games. By 2008 the rushing offense was in the 20s somewhere, and its hard to argue that Ben was remotely close to a system QB. Finally, I would again point out the 2000 Steelers, who had the 4th ranked rushing offense, the 6th ranked defense, and no Ben, and didn't make the playoffs. Thus the Steelers also support the overall trend that you cannot win Super Bowls with "just" a system QB, although you can do reasonably well.
Looking forward, if Ben is suspended there is little more than a minuscule chance the Steelers can contend for a Super Bowl in 2010. You can't reliably use the rushing/defense formula to get to the SB in general - it hasn't worked in over 5 years for anyone - as well as with the Steelers in particular.