The offense and defense need each other to be successful, saying the defense needs to create turnovers to give the offense a short field is recognizing the fact that the offense isn't that great and need help.
Saying that the offense needs to sustain drives to keep the defense off the field focuses on the fact that, regardless, of their ranking the defense didn't really achieve that ranking in crucial situations.
Dick Lebeau is as good a DC that there is in the league, bar none, he still needs players to make plays and they didn't last year. This year remains to be seen.
Todd Haley is a good OC, maybe not the best or one of the best, but he's near the top and, like Lebeau, he needs players to make plays.
Each coach only needs to put players in a position to succeed which IMO they both did and in those situations the players let them down many times last year.
Blaming the OC or DC for the Steelers woes last year is like blaming the forn and knife for being overweight.