I came across this question: https://webapps.stackexchange.com/questions/19013/is-it-okay-to-modify-a-quote-you-are-re-tweeting-if-its-too-long today. Though, it deals with the usage of an app (Twitter), it seems more about practices in social media. So does this have a place on WebApps?
I'd say not.
As you say it's not about anything technical, just the social niceties of how to edit someone's Tweet.
Using the tools of social media, which are often web apps, would be on topic.
How you conduct yourself and what you publish would be off topic.
It's as off topic as asking on Gaming if people should cuss back the 12-year-olds they're getting into fragfests with.