Exactly. The "iron law" doesn't seem to apply. There are only three kicking specialists in the NFL Hall of Fame who didn't play another position and one of them, Andersen, did not win a Super Bowl. The only other placekicker was Stenerud, who had credentials far beyond any of his contemporaries. That simply isn't true of Gostowski. He had some truly great seasons, but not that many in the context of the long career of a kicker. The rest of the time he was very good, but not at the top of the game.
Tucker has a better case. He has arguably been the best kicker in the league since he arrived in 2012. As a rookie, he made 30 of 33 field goals and he was perfect on extra points for the Super Bowl champions. He has a better field goal and extra point percentages than Gostowski and puts a much higher percentage of his kickoffs into the end zone. Given the committee's history of not respecting kickers, I doubt both guys get in. If that is the case, it's going to be Tucker.