One unsurprising result here: there are fewer goals scored in the playoffs than during the regular season. If you're down by three in the second during the regular season, you'll probably rest your best players to keep them from getting hurt in a meaningless game. In the playoffs, there's no point, and no giving up.
But the OT scoring levels are surprising: throughout the 1970s and early 1980s, teams apparently played more offensively in overtime than they did during regulation. But the opposite has now been true for more than 20 years.