It would probably be only marginally more expensive (for Twitter specifically) for them to add changes in a way that's backwards compatible with older clients, so I don't think this argument is particularly convincing. I think, because it's somewhat plausible, they pushed it, but because they really wanted to control all of the clients, to increase their advertising revenue.
Of course it depends on the nature of the specific change. I'm sure lots of developers really appreciate bug fixes, especially for bugs they've encountered, let alone developed workarounds or patches.
But there's a reason (really, lots of reasons) why it's a great idea to pin one's third-party dependencies. Change is, at least, costly; at beast trivially so (but never literally nothing).
Yes, and customers do very much vote with their wallets, even when the costs of switching exceed the benefits of switching!
What kind of bike, or most other physical products, get updates or upgrades for free whether one wants them or not? Certainly physical products with software and networking can, but people are often upset when that happens anyways. I'm pretty sure almost all bikes are not in fact automatically updated or upgraded after they're purchased. And that's essentially a 'feature' now in comparison to a lot of software purchases.
How would a Facebook group really work any differently than a subreddit? They're both just names. There are no 'categories' on Reddit; just good (better) names.