Remember that the ratings system is just a commercial tool to keep movies from being boycotted or causing other harmful controversies.
I really do think public attitudes have become more strict. Remember that in the 80s and early 90s graphic R-rated blockbusters were marketed to kids with action figures and video games. Now Hollywood barely ever makes those kinds of movies so it's harder to compare, but I don't really think that kind of marketing would fly. By the late 90s the figures they made for movies like that were marketed to older collectors.
Not for children under 17
Although admittedly they still make kids toys for PG-13 blockbusters.
Also I think theaters are stricter now about letting high school kids into R-rated movies without and adult. Nobody cared at the theaters where I live when my friends and I were in high school. But my sample size is obviously small so maybe that generalization doesn't hold.