There really is a sub-network within Twitter of people who only ever have nice, productive conversations with one-another.

This sub-network seems to have a lot of overlap with the set of people who use their Twitter handle as a substitute for an email address—i.e. the people who want you to tweet at them if you want to collaborate with them on something. Which itself is vaguely overlapping the set of people who are "famous", but not celebrities—i.e. people who are well-known names in their own industries or hobbies.