My memory may be a bit hazy, but didn't the Steelers beat the wild card Cowboys one of those times pretty handily? The Cowboys beat the Vikings in a playoff game that featured perhaps the worst playoff call of all time; Drew Pierson pushed off on the Vikings cornerback on a prayer hail Mary pass towards the end of the game, catch the TD and the call was on the VIKING player?
Also, as you pointed out, the Rams beat the powerhouse Tampa Bay Bucs to earn the right to get smoked by the Steelers and the Vikings, sorry to report were the Buffalo Bills of the 1970's, getting to four Super Bowls and not being in a single one of those games, losing to the Chiefs (that team may have been the best Viking team of all time by the way), Dophins, Steelers and Raiders.
Not to take anything away from those Steeler teams of the 70's; Chuck never lost a Super Bowl to a NFC pretender now did he, 4-0 he was, a true HOF coach.........