There's no doubt that the calls benefitted the Steelers but reading this thread here are a few comments to keep in mind.
Myth 1) Seahawks totally outplayed the Steelers yet lost because of refs. Not True. Seahawks had 396 yards, Steelers 339. Steelers 8 - 15 on third down, Seahawks 5 - 17. Early in the game, the Steelers were outplayed but that evened out in the middle of the second quarter. Both teams had big plays (Seattle INT for 76 yards, Steelers run for 70 something). Steelers sat on the ball a bit after the Roethisberger INT while Seattle was playing from behind - passing typically generates more yardage.
Myth 2) Fourteen points were taken away and if this had not happened, the Seahawks win 24-21. Obviously not true. Four points were taken off the board (TD traded for field goal). Without the holding call, Seattle was at the one but not guaranteed points. 3 to 7 were likely but even with the 7 you still just get an extra 11 points total. Finally, Steelers game plan would have been different if they didn't have an 11 point lead.
Bottomline, better referees would have made the game better but to say the Seahawks would have won is simply not true.