I think they have more things in common than they have differences. At they end, you also have a story, i.e. a linear series of events, you can tell each other after the fact.
I feel most of what David Perry describes above also applies to other games that are about "playing to find out what happens". Very few that I know are about playing out a prescribed story.
For example, if I were to write a PbtA OSR game, I would say the MC section should have something like this:
- to engage in creative problem solving.
- to keep the future unpredictable.
- Employ and reward player ingenuity.
- Try to be impartial in your judgement.