Hey, that was me! I guess I could reply, huh?
I don't think there's any difference. It just varies, but I think it varies based on their willingness to be friends more so than their preferences for "romantic relationship models" to come as monoships or polyships. It's more about the people involved and their willingness to stay in relationship after the end of the romance balanced against what brought the termination about.
Some people are just bad partners and bad exes. If it ended because they beat you up every night -- you do NOT need to be in relationship with them after! You may want to be, but it is just not healthy for you to do so.
If they cheated on you, you may not want to forgive them, much less be friends later. YKWIM?
But if the reason for parting was something not so ugly -- like it just not being a runner after the initial dating time or loving once and then growing apart...
Some people want to be good exes and just that. So if they bump into each other will be polite. But they don't take special pains to hang out together and include each other in their lives any more.
Some people want to be good exes AND friends, so they are more willing to do more than "basic polite." Maybe just a bit more, maybe a lot more. The "friends" spectrum is wide.
Sometimes they have kids together and need to coparent, so try to be friends to make that coparenting relationship easier. Certainly makes it easier on the kids if they can manage to be!
Now I wonder, are there any broad differences in attitude about breakups? Would I have received different feedback from a poly forum verses other groups?
There I would have told you "Why are you asking me? Why don't you ask yourself what your feelings are? Want to be friends with your ex? Be so then. Dating partner can take you as you are. Or not.
Or ask your dating partner what her feelings on the subject are? Maybe she would be bothered and would prefer not to date you if you are friends with ex. Maybe she doesn't mind and figures that's your post divorce biz to handle.
Me? I do not mind either way. But asking YOU or asking HER makes more sense than asking me, because who is in romantic relationship here? YOU AND HER."
Just my 2 cents,