I just wonder if some of the 'abuse' referred to is just not agreeing with someone's point of view!
Well, yes and no. As we have seen from these fiery threads, some adult children and their parents have conflicting points of view on what constitutes abuse. That's normal enough. It's a rare abuser who says "hands up, I treat the people who love me like I am the God Of Everything and they are acolytes who must please Me or be corrected." But most abusers think like that, though I'll give myself some credit for creative expression 
The sad part about it, imo, is when they're incapable of seeing how this looks from a more 'normal' perspective. But incapable = genuinely not able, so there you go. It's an impasse. The only thing to do with an impasse is take the other road, even if it goes in an unexpected direction.
If you mean they fell out over ideological differences - it can happen, yes. I have a comparable story:-
A friend of my family is a white supremacist. He really believes in what he says, which is stunningly racist, and loves nothing more than expounding his "logic" to a captive audience at dinner. Having tried every approach from delicate to blunt as a mallet, and been dismissed, I simply told him & his (very adorable) wife that I find this distressing to hear so will choose not to in future. Cue dinner at their house: he launches into his theories; I quietly excuse myself and go outside for a fag. He was outraged! Utterly fuming at my disrespect for his opinions. Told everyone they know about my abuse of his hospitality, shocking manners, and ingratitude. This was years ago and he still avoids me as much as possible.
What if he was my father? His views really are obnoxious. I find it hard to believe anyone seriously thinks skin colour denotes intelligence & competence, but he does. I would still have had to walk away. He would still have dismissed my feelings as irrelevant. We'd still be limiting ourselves to polite greetings ... and he is the offended one, remember? People might think it awfully sad that his daughter avoids him, but what to do? Families do divide for ideological reasons sometimes.
I can't imagine you think they may have fallen out over a difference of opinion about what style of pushchair a GC should have, or anything like that. Happy families have successful conflict resolution strategies. Nobody reaches adulthood without having big rows with their parents (usually starting at 18 months, and repeating on a regular basis to 18 years
) Happy families know this, and get along just fine.
No-one would break up a happy, well-functioning family relationship over a petty row. They know how to get past that. The narrative of a broken family might sound like it, though. Their conflict resolution may always have been poor. One party may always have got their way. The habitually losing party may have cracked at the final dig, however trivial in isolation, and gone "No more!" You know, the straw that broke the camel's back.